Automation is programing parameters on volume, pan, effects, etc. to change automaticly at the point you specify in a song.
Most of the time you play the song with "record automation" enabled. As the song plays you make the changes you want, in the places you want.
Then simply shut off record autiomation and the next time you play it, the adjustments will be made automaticly just as you recorded them.
A volume envelope is a type of automation that uses a visable line that can be moved up, down, curved, etc with your cursor to control volume changes on a track throughout the song. Panning of tracks is also often done in this way.
F.S.