Hi i just installed a mod into my game and its a BMW but its says its installed but how the hell do i find when i am playing huh please tell me??????

Presumably you have some picure of the car?
You have to find it ingame.

If you know which car you've replaced by the BMW and you know where those cars can be found then go there.

There's a list of where different cars spawn somewhere and where particular cars are found. Check the FAQ for car info.

If there's any readme.txt for this mod then that might tell you where to find the car.