Mac Gaming Mods

Hello I have just a few questions about mods.

1)Do I have to have the game I am downloading mod for?
2)Do all I have to do is play game and I can make it the way I want?
3)I know I download features to make other stuff but how do i customize the game while I am playing it?

1. Not sure what you are asking on this one. Do you need the game to play the mod? Yes.

2. Yes, you can change what options the server has set if you are hosting.

3. Are you asking how you can mod the game? If yes, then you need a PC to run the various mod programs.