1. Go to tf2center.com
2. Sign in through Steam
3. Click "Play now"... or whatever it says, just click that thingy next to the bird
4. Select a server (I personally recommend you Highlander)
5. Pick the class you wanna play
6. Turn your sound on, because when everybody joins the lobby you will be hearing a Heavy saying "Who is not ready?"
7. Ready up
8. When you hear "Let the games begin!" you have to click the reconnect button or something that pops out on your screen

Note: On payload lobbies there are 2 rounds, so don't leave when the first one ends and you play to 5 wins on cp maps. Also on koth maps you play to 3 wins without timer.
Tip: Make sure you have 90 fov. If you are not sure, just type "fov_desired 90" in the console. If you don't know where to enable console, try Googling that. It's very easy.

Sorry for my English and sorry if there are any mistakes.