This has actually been answered by Jon Peters (if I recall correctly, but it may have been another developer) in the now defunct official GW2 forums during beta weekend #3.
In his words, in WvW /map and /team channel are currently implemented to be absolutely identical. This of course means that enemy worlds can not read the channel. (He also elaborated on how ANet had planned to disable one of the channels in WvW for the sake of clarity, but this turned out to be more complicated than initially thought, so they left them both in the build.)
Unfortunately, I cannot give a link to post since the official forum has been wiped again after the end of the beta weekend. Also note that this is information regarding a beta build, and things may change before launch.
This may be something other than what you are looking for, but the main thing is going to be to practice. PvE can help to some extent, but you really need to just get in there and start playing. That's the only real way.
I understand you're possibly nervous about not being able to contribute for your first couple times in PvP or WvW, but that's really just how it's going to be. You will get much better much faster by actually playing. People probably won't even notice, and even if they do, it's just part of the game.
Beyond that, the biggest piece of advice I can give is to be familiar with your skills. You will tend to get nervous in PvP, moreso than in pressure situations in PvE. Make sure you are familiar with your CC effects -- which skills they're on, how they work, how long between uses, that sort of thing. Again, gauging how effective each skill is will only be able to happen through actual experience.
Other than making sure you know how to use all of your skills (with focus on CC), you'll want to practice kiting -- again, this is best done against other players, but you can try kiting mobs around as practice.
Familiarity with other classes/skillsets will help -- I suppose you could try playing with all sorts of weapons/classes/races so you will know ahead of time exactly what to expect from every opponent. Jumping right in will still be a faster way to gain this knowledge than trying to prepare without actually PvPing.
Best Answer
For starters, you should look the map for a commander if any is present. If so, he should be giving the orders (if he's a good commander and not just someone who wants to show his shining blue icon).
If no commander is present, people usually gather in "buses of player", in order to raid places with a massive force. It's usually a good group to learn WvW as well as doing things with lot of successes.
Eventually, you will want to do something on your own. If so, be sure to bring some friends along in your party. There are some thing a small group (or even a single person) can do:
Don't feel oppressed by the player giving orders on the /map, you can contribute to it yourself. Don't hesitate to ask questions too, many players will be kind enough to help you.