well that not really detailed.. so.. umm..

when you download them
1. make sure that they are in your mods folder
2. make sure they are .tbm
3. there are 3 ways to play mods:
- you can use toriluanch (which is in the 1st post of my suggest a mod thread) even if your not registered
- you can go into the menu in-game and click "mods" can scroll down to the mod you want
- you can type: "/lm [mod name].tbm" by pressing "T" in-game. example: /lm sumo.tbm

if nothing works tell me =D