How To Learn To GM
There are a variety of resources nowadays that can help you accomplish this. There are also many existing questions on this site about GMing that will point you to more content than you can ever consume.
In your question, you mention wanting to see more examples of real play. There's a number of ways to do so.
Actual Play Resources
- Podcasts capture the entire play session. There's video podcasts too like on Twitch. See Where can I find actual play podcasts for RPGs?
- Session Summaries (aka Actual Plays, Story Hours, Campaign Journals) usually are severely abridged, but leave out a lot of the cruft. See Where can I find transcripts of actual game sessions? and Where to find game session reports?
- Blogs. There's a million blogs about how to GM. Start with the RPG Bloggers Network. Go to the blogrolls of blogs you like to find more like them. Focus in on blogs about your chosen game(s) and play style(s).
- Play by post forums. If you want to watch people actually play in text, there's a million of these too. Many dedicated sites, specific forums on RPG.net, ENWorld, Paizo, etc. In fact, RP-by-post is very popular even when not affiliated with a proper RPG/ruleset.
- Sit in. There are plenty of other people running games, some in public places like your friendly local game store (D&D Encounters, Pathfinder Society) and conventions. See below under "Play" though, if you're going to the effort of being there you need to stop being a wallflower and get on in and play.
Some games also have better advice sections than others - see What role-playing games have good gamemaster advice sections?
In the end though just watching is not the most effective approach to learning. Watching games is less useful experience than actually being in one. Have you considered playing in those games before running them to learn from other GMs? It's reasonably easy to find other gaming groups, you don't have to abandon yours to play in another. Where can I find other RPG players?
Go to RPG conventions, find games at gaming stores, play on forums or G+ (see also Finding online RPG players for a play-by-chat RPG Campaign?) - just get more experience. The GM was often called the "judge" in the old days, and in the legal world you need to spend a lot of time being a lawyer before you make a good judge. You need to spend some time playing to become a good GM. If you can't think how the players will proceed in a given situation, you need more play time.
There are many books on GMing - see What is the single most influential book every GM should read?
Also try watching/reading relevant genre media. "I don't get how to put together a story" should get its first-order correction by consuming some of that genre and looking at the stories.
A lot of the problem you seem to be experiencing is pure storytelling. Try How do I get better at narrating/storytelling as a GM? and As a GM, how can I create and role-play diverse NPCs better? Read up on the specific aspects of GMing you feel you're not good at, there's plenty here. Try questions tagged with the gm-techniques tag. Feel free and ask questions here as well about specific aspects of GMing.
There are also a large, large number of RPG forums out there in the world, for every game and type of gaming. If you don't understand something someone posts, you can easily reply and ask.
aka How I Learned To GM
We didn't have these newfangled Interwebs when I was a kid. I GMed almost before I ever played. I did play in a very informal game of D&D in a car on the way to Scout camp, no dice, PvP, everyone had artifact weapons. But other than that, I started out as a GM. I bought a sci-fi RPG (Star Frontiers) without knowing anything about it (I had bought and played a little TSR chit game, Star Force, and was looking for other fun stuff from the same company). None of my friends were interested in GMing and I was in a small Texas town that didn't have conventions or whatnot - life was less mobile and connected back then. So I just read the game books and then ran games for my friends. And I kept running them, and learned from my mistakes and corrected. I read comics and science fiction avidly, so characters and plots weren't that hard to devise. Beyond that, I just learned the way you learn to do anything through practice, whether it's a sport, writing, a musical instrument... How-to's and YouTube videos are cute jumpstarters nowadays, but "Do, and learn from doing" has yet to be eclipsed in being the primary way to actually become good at something.
Fear of "making a mistake" is the dumbest and most paralyzing instinct you can have in life. In a video game you're going to die a couple times off the bat; in baseball you're going to swing and miss a lot before you hit; in baking you're gonna burn some cookies. But you learn through those mistakes. It's fine to do a little reading up ahead of time but the only way to become good, really, is get your butt in gear and do it.
Dungeon World encourages GM improvisation, but does not discourage preparation
Dungeon World discourages an on-the-rails style of campaign where the players are simply there to work through the GM's plot.
In the GM section, the authors emphasize improvisation (to run Dungeon World you'll need to adapt to the decisions your players make as they move through the world) but Dungeon World is not purely about improvisation.
If you look in the Dungeon World materials you should see sections for Fronts and The World.
I feel like you either glossed over these sections or missed them entirely as they really serve as the foundation for creating adventures and plotlines in Dungeon World. Be sure to study them as they contain a lot of information and GM tools/mechanics, much too much for me to go over in a single answer.
Fronts are how you as a GM organize challenges, goals and risks to the players.
Fronts are secret tomes of GM knowledge. Each is a collection of linked dangers—threats to the characters specifically and to the people, places, and things the characters care about. It also includes one or more impending dooms, the horrible things that will happen without the characters’ intervention. “Fronts” comes, of course, from “fighting on two fronts” which is just where you want the characters to be—surrounded by threats, danger and adventure.
Fronts are built outside of active play. They’re the solo fun that you get to have between games—rubbing your hands and cackling evilly to yourself as you craft the foes with which to challenge your PCs. You may tweak or adjust your fronts during play (who knows when inspiration will strike?) but the meat of them comes from preparation between sessions - p. 185
There is even a helpful little checklist:
Here’s how a front comes together:
Choose campaign front or adventure front
Create 2-3 dangers
Choose an impending doom for each danger
Add grim portents (1-3 for an adventure front, 3-5 for the campaign front)
Write 1–3 stakes questions
List the general cast of the front
Campaign Fronts represent overarching threats/plotlines between multiple sessions. Things cooking in the background while the adventures go on. "One Ring to Rule them All" serves as a good example of a campaign front from the Lord of the Rings.
Adventure Fronts occur in the here and now, they could be a place or a direct threat to the party. The Mines of Moria would make a great Adventure Front.
Dangers are the creatures, places, or things that constitute the threat of the Front and get to make moves just like monsters or players would (But only you the GM knows what moves they are making, the party only sees the effects).
Dungeon World's setting lends itself to all kinds of heroic stories
The generic fantasy setting of Dungeon World should be easy for your players to latch onto. It bears a lot of similarities to what they are used to with Pathfinder. Just because the world is similar to a Pathfinder/D&D style setting doesn't meant the adventures your players have are required to be just as similar in their approach. Exploring ruins can be less about killing monsters and avoiding deadly traps and more about puzzle solving and discovery. Saving a kingdom from military defeat doesn't mean the party single-handedly kills the opposing army, but maybe they manage to go boost morale, find new supplies, and help train new recruits.
The World section in the book goes heavily into how to create towns, cities, ruins, and wilderness for your players to experience, how the actions the players take and those they don't should affect the world, and how the world might be affected if various fronts resolve.
Anyone can attempt anything
The Dungeon World resolution mechanic of rolling 2d6 + mod with the static ranges of 6 or lower = Failure, 7-9 = Success with complications, and 10 or greater = Complete success means that characters can always partake in problem solving and trying new things. In fact Dungeon World rewards risk because the best way for characters to gain XP is by failing rolls.
You're most certainly not here to tell everyone a planned-out story.
And you've felt that friction trying to make it happen, haven't you? Walking into a scene with a point planned for how it's going to end, and you have all this power to deal damage and put people in spots to do it. You feel a bit of a bully, and you should.
The thing with Powered By The Apocalypse games is that they're not great for telling stories "by accident", such that they arise as a result of fixed game rules interacting in unpredictable ways without anyone's intent to create them. Or "by 'accident'", where you as the GM contrive without your players' input or knowledge to present rules in such a way as to force a particular outcome, regardless of what your players do. They're for telling stories on purpose, with the full participation of all involved.
So how do you get your PCs to walk into their own deaths on purpose?
If it's the premise, you don't have to play it out.
If the interesting part of your campaign is going to be working as agents of cosmic powers in the afterlife or as time-displaced heroes in a strange new future, you can just start there. Even level 1 characters don't start at the very beginning of their heroic journeys - they've set up cons, guided each other through the wilderness, heard stories about each other.
If it doesn't make sense for an agent of cosmic powers or the last hope from the distant past to start out as level 1, they don't have to. You know what a higher-level character looks like, just add some stat points and pick some extra moves. Equipment and money and magical gear aren't nearly as important to Dungeon World as they are to other games, so your starting loadout there is fine to keep.
If it's important that some things have happened in their past that will play forward into the adventure - you know, like how exactly they died - well, that's what adventure moves are for. They were called "love letters" in the original Apocalypse World, and honestly I like that name a bit better, but you can read up on them in the Advanced Delving chapter. They differ from other player-facing moves in that they don't have to flow out of a player's narration of what their character is doing; in fact, they don't have to be freely available to the players at all. They reflect a unique circumstance, assume some narration, and influence how events play out over a longer period of time.
So for example, here's something you might set Wizzrobe up with:
Or, here's something you might just hand out to everybody as an ongoing concern.
If it's a development in the middle of an existing campaign... you still don't have to play it out.
It might be a bit harder of a sell to people who are invested in their characters and the world as it exists in front of them, as opposed to just starting a campaign with that premise. But you'll still need to sell it to them, and you'll need to be willing to walk away from your idea if your players don't buy into it, because you're still telling this story on purpose.
The adventure moves are still how you'd make the transition to the new form of your campaign, because otherwise you'd be walking into a scene where your players could theoretically act freely with a plan for how it's going to end, and we've already established that's a bad thing. Adventure moves that you deploy in this way are at once easier and harder to write than they might be for a campaign setup. Easier because you've been playing in this world for a while and you know what kinds of things your players care about that you can place in the crosshairs of a "how you died" move. Harder because the adventure moves are part of the sell and you need to be more open to negotiation with your players about what's ultimately at stake.