This is predetermined for each character. Translations All of Battle of the Millenium's new client commands are in the configuration screen, but in French. Most of the standard HL control functions can be intuited rather easily, but some of the new commands require some clarification. If you need more help, I recommend using The Babel Fish . It's better than nothing.
Some characters can fly.
The answer depends on your play style. The VGUI has important information for all the classes, so take the time to read them very carefully. Of course, nothing is a substitute for actual playing around with the various weapons and powers. As a result, don't be surprised if a full-bar blast from Superman's heat vision doesn't kill an opponent outright. Each character has a good array of abilities and weapons with which to wreak havoc on one another, and there's plenty of in-game documentation available if you forget what's available to you.