Peter, try this link -
http://www.drycreekphoto.com/Learn/m...alibration.htm
The info is a little old as they make references to dated puck hardware (i.e. Spyder etc), however the principles are the same. I would only worry about calibration if you're looking to produce the best possible prints from an accuracy point of view or in general you're quite critical on colour. Its not something you simply perform once and forget about it. Its a methodical process that needs to be performed regularily to ensure accurate colour presentation.