Getting off the board, and actually playing a game is pretty simple. You just sort of do it, run to a bunker you think you can make, and then let the game play out.
There are some things you can start working on immediately to help yourself. First, start working on being comfortable with shooting your gun in either hand. Second, be facing downfield, and ready to shoot at all times, as the name implies, the game happens fast, you've got to be ready. Generally you should meet some other players who are willing to help you out, a lot of times, all you've got to do is ask. Third, shoot your gun, A LOT. A gun that's not shooting, or at least attempting to find a shot may as well not be on the field. It's rare that you'll be in a situation where you are completely pinned and can do nothing. If one guy is shooting at you, find a different guy to shoot at, and pull that trigger. Watch, talk, and listen. Watch for opponents, tell your teammates where they are, listen for your teammates to talk to you. A lot of speedball revolves around communication; where are the bad guys, what are they doing, and what can you do about it?
Aggression. A lot of new players tend to be passive. It's important to understand that inaction, is still AN action. Doing nothing takes you out of the game, and allows the opponent free reign to do what he wants. If the bad guy is dictating the terms, he's probably winning the game. Aggression isn't always running down the field, or bunkering guys, it's as simple as refusing to be held down, actively looking for shots, and bumps(moves). Even a back player can be aggressive, just by controlling his zone, and staying on his gun. When he is railing out paint, and stopping the opponent from shooting, or gaining ground, he is aggressively dictating the terms of the engagement.
The following pictures should help with bunker names. They are listed on the side of the first pic. The second should give you an idea of what those bunkers look like in 3 dimensions.