It's just simple:
1. Choose a weapon name, then the weapon associated to it.
2. You'll see "models" and "sound" inside. Place both of these in the root folder of TFC, where you'll see the same folders.
DON'T FORGET TO BACKUP YOUR ORIGINAL FILES, IF YOU HAD ANY!
3. The "required" folder is needed alongside all weapons. It has the muzzleflashes and sounds needed for the full experience of this pack. Drop the sound and sprites folders on the same place.
There and there. Easy and simple. The rest is up to you, just pick your weapon and wield it as you pump some rounds into your opponents.