Need tutorial about mastering.

[Smag]

This may help you

http://www.amazing-demo.com/Articles/mastering.html

Recurring themes seem to include being subtle with the effects and only use tools / techniques if you need to, not because you think you have to. Have a commercial CD to compare your tunes to and flick between the two to see what needs to be changed / added. It's important hat your tune can stand up on it's own without mastering, if it doesn't then you may need to strip it down again. Mastering is basically about creating consistency and balance in your tracks so the listener doesn't have to get up to change the volume or graphic EQ on their stereo.