A tv tuner opens up using a program from your desktop. It is no different from opening microsoft word or photoshop or whatever, except instead of a blank document showing up, tv does.
For recording shows you dont need anything but the tv tuner. For watching movies from tv, you just change to the channel its playing on. To record lets say your ps2 onto your computer, you would need some sort of input device on your tv tuner, whether it be composite, s-video or component.
You hook the tv tuner to your coaxial cable/satelitte cord.
Get a haughpauge (or h/e u spell it) pvr. They are great. Honestly.