rebuilding front disc calipers

i just rebuilt my rear disc, and it was really simple. just the square seal and the dust boot. when i went to look at rebuilding my front disc there were more parts in the pic at the parts store. what all is involved in rebuilding the front disc brakes??
Your mention of rear disc only adds to the confusion on this end.
I've never rebuilt a disc. I have rebuilt several different types of calipers though.