Each mod thread has its own instructions on how to install whichever mod you're looking up. If you're just looking to do ATP, this should be all you need: topic29-18104.php
As for the controls, I'm not entirely sure if this is correct, but "Fire 1" is your standard shot. On an Xbox controller, I recommend mapping it to "A". Then "Fire 2" is your slice, as well as drop shots and defensive lobs. I'd map that to "X". Then the combination of BOTH buttons is your "acceleration" or "aggressive groundstroke" if you have a short ball you want to attack. This can also be mapped to one button, so I recommend the right trigger or right bumper.
And then, of course, map the "Menu" function to the "Start" button. There should be "Control Options" right there on the main screen when you load it up.