Release, Attack, Threshold.

[mattdee1]

Its mainly for the different levels isnt it as if i start yelling in the mic it would bring it down a notch or so.

Like somebody already said, you'd probably be surprised how far a good mic technique will get you. I definitely learned that lesson the hard way.

If the points where you start "yelling in the mic" are occurring at convenient times--for example, when your song transitions from one section to another--a quick and dirty cheat is to record the vocals for those two sections on different tracks, so you can set their levels separately in the mix without having to bother with automation. Of course, this trick is of no use if the fluctuations are happening randomly throughout the song.