Overwatch – Tips for Defending on Assault Maps

What you are looking for is the Custom Game option in the Play menu. You can choose the map, the map rotation, the difficulty and amount of AI players, etc. This should allow you to play privately or with friends in order to increase your knowledge of maps and heroes.

http://overwatch.wikia.com/wiki/Custom_Game

Edit: As to how the youtubers and others fly around the map, they use the custom game menu, and when viewing the team lineups page, they right click on their name and swap teams to the Spectator team. Then they start the match. This video shows how it can be done at around the 10:00 mark:

1. Assault

   Temple of Anubis Pretty difficult but not impossible. Right at the beginning as an attacker, you may have someone on the far left side, trying to flank you and not let you reach the first choke point. I've been able to push a Torbjorn once with Phara

   Volskaya Industries

   1. At the start, at the attackers spawn you can get some kills as either team as one side of the map is entirely open.
   2. Also open is the entire area behind Objective A.
   3. Either far side of Objective B

2. Escort

   Route_66 At the beginning, some heroes might try to flank on the right attacking side, and up until the first checkpoint. I've been able to knock heroes out of the map from there.

   Gibraltar Again only at the start of the map, on the left side, when attacking, you might be able to get some free kills.

3. Hybrid Maps

   Numbani Most of the flanking routes aroudn the map are fairly open. Specifically I enjoy the left side (as an attacker) of Objective A, you can get ALOT of kills there as either team.

4. Control

   Ilios

   1. Lighthouse. By far my favorite. As either team you can basically get a kill every time you feel like it. If an enemy is on the control point but towards the back edge, you simply need to be at the right position to get the kill. Also when the enemy is trying to enter the control point you can push them off the edge.
   2. Ruins By far my least favorite. I know its possible to get a kill towards the open end of the map, but so far I've been unable to do so.
   3. Well As the name of the sub map suggest - you can get enemies in the well. Roadhog Can be helpful in this specific case too. If you hook the right ad the edge, when the hook releases, they simply fall.

   Lijiang Tower

   1. Control Center The least possible position to get an environment kill. You need an enemy to be flanking from the elevated side and even there it's not too easy.
   2. Garden and Night Market both have a ton of open areas where you can score your kills, mostly on routes leading to the control

   Nepal

   1. Sanctum Half of the side of the control point is open, a good position from you, is almost certainly a kill. Phara would do a bit better as she can fly up and get a better shot, especially when you need to clutch the control.
   2. Village one of the sides is open, and alot of the heroes would try to go for the medkit. You can score a kill then. Also possible when heroes try to enter the control point from that side. Also slightly less common is a sniper from the far back. I had a fairly intense fight with a Winston once, he pushed me twice but Hanzo can climb walls. He finally had to use his ult to DPS me to death.