I'm happy to know that I'm not alone in sucking at TF2. I swear everyone is twice as fast and twice as accurate as I am.
The only class I'm ok at is Pyro, and it's considered a noob class.
Anyway, here are some tips that might help you feel less overwhelmed:
- Watch "How to play" videos on Youtube. Especially for Spy and Engineer since they can be somewhat confusing when you start.
- Play on an empty server at first. That way you can learn the maps and some of the class skills without getting killed.
- Keep watching people play. See what the players at the top of the board are doing.
- View the Commentary. It has a bit about each class.
- If you have the patience, go here:
http://tf2wiki.net/wiki/Main_Page