Where do i Install mods at

Well, I think that would depend on the game you're playing here and the kind of Mod you want to apply. Unless I'm mistaken the good folks here haven't evolved to super human telepaths who can read your mind. Could you elaborate a wee bit on what mod, and what game?
As a general rule of the thumb, it's a good idea to always look for a readme file, they tend to be more or less self explanatory and are usually included in mod downloads.