http://www.fortress-forever.com/wiki...7s_Guide_to_FF
Wiki Article written specifically for you. Explains FF differences in terms of TF2.
Main points - Each class has grenades, which rule.
Bunnyhopping keeps things fast, jump queing helps.
Movement skills are essential to the game, especially for offensive classes.
Read through the wiki to understand the different grenades and movement skills. Everything else should be easy to pick up just by playing.