I've downloaded 2 mods, but I've no idea where to extract them to?
Well, I have Win 7 so hopefully what you have is similar.
First you need to make sure you can see hidden files under your folder options.
Next, navigate to C:(or drive you installed to)/Users/(your profile)/AppData/Roaming/runic games/torchlight/mods
Simply extract or copy the relevant file to that 'mods' folder and restart the game.