Sketchup Snaps question

Learning how to use sketchup, I'm just playing with models from the various builds on OpenBuilds.

I can manipulate parts ok, but for one thing:

I can't figure out how to snap parts together in precise alignment based on a set of points. .

For instance, how do you make a bolt object snap to the center of a hole with the face of the bolt head flush with the face of the surface where the hole is located? Or how do you snap 2 objects together so their faces are in contact and the are...

Sketchup Snaps question