Rocket Jumping is the act of looking down, jumping, and firing a rocket at the same time. This will propel you in the air like in almost any cheesy action movie hero after a large explosion. Some games don't use the rocket launcher to rocket jump, so experiment. An example is Half-Life, where the Gauss Gun is used to 'rocket' jump. It's also possible to use the BFG10k to propel yourself to insane heights.
Timing is hard, because of the pre-fire delay.
That depends on the game. Check your games documentation for more info. Start the game, then bring down the console. Then start up a Q2CTF game and it should work. Once you put it on, all your saved games aren't compatible.