It depends on which mod you're trying to install. There is no one set procedure. If it didn't come with its' own installer then you'll need to study the mod 'read-me' file (which should be included) ...

to me it looks like the bodies flop around a bit more. i don't think that the game needs more bullet time though, overusing it makes the game not a challenge. not a mod i'll be getting. now an updated ...