Compass and Altimeter Basics
The following links provide an overview of how to use a compass. By following these links you will learn the parts of a compass, how to make basic compass readings, and the importance of understanding declination.
Using a Compass (more advanced) Note: site contains other nav info, some of which is confusing or not applicable to AR. Clicking "next page" link they provide will guide you through the valuable compass section.
Note, that if you start doing longer races, you'll want to invest in an altimeter as well. (Often an altimeter is a more useful tool in an adventure race than a compass. Altimeters are fairly easy to use, and there are several styles available. Altimeters need to be frequently calibrated, and should be calibrated EVERY time you find yourself at a known altitude during a race.
Buying a Compass
You don't need a high end compass to get started in adventure racing, but you do want a compass that "settles quickly" (the needle will point north quickly) and has an easy to use adjustment for declination.
A good entry level compass is the Brunton 8010G.
For a high quality AR-specific compass, consider the Brunton 8096AR.