What do the camera’s AV files, M files, and TV files mean? What are the functions of each?

AV is aperture priority, which means you set the aperture value of the lens yourself, and the camera will do everything else automatically. TV is shutter priority, where you set the shutter value yourself, and everything else will be automatic. M mode is fully manual, and the aperture, shutter, and sensitivity are all set by yourself. Most photographers like to use M mode, because this way the camera completely listens to itself, and automatic ones are sometimes inaccurate.