http://www.tonypool.com/resources/IR...otes+-+NDB.pdf
This one does an OK job to get you started. Be careful of the nomenclature though. We don't track an ADF. We use an ADF to track an NDB.
Also, learn to fly both fixed-card ADF's, movable ADF's, and RMIs for the same reason as you learn to drive manual transmission. Indeed, starting out with explanations on a fixed-card ADF often helps some students understand the basics, before moving into using a movable card, then bringing in the RMI.