To properly setup up the cams, they must be “degreed”.  Degreeing a cam is the process of synchronizing the position of the cam to the position of the crankshaft.  The timing belt runs from the crankshaft to the cam gears, which means that once installed, the relationship of the cam position to the crank position will not change.  This is where the adjustable cam gears come in.  The adjustable gears allow the cam to rotate independently of the crankshaft, and this adjustability is used ONLY during initial setup (degreeing) and dyno tuning.  The adjustment is performed by loosening the screws on the face of the cam gear and turning the crankshaft by hand.  The crankshaft will turn the timing belt which will turn the cam gear’s outer ring, but not the inner ring.  Since the inner ring is what secures the cam gear to the cam, the cam will not turn.  As a result, the crankshaft has turned but the camshaft has not.  You have just changed the positional relationship between the camshaft and the crankshaft.  Once complete (adjustments are typically done in 1-2° increments), the bolts on the face of the cam gear are tightened, which locks the center portion of the gear to the outer portion, thus locking the positional relationship of the cam gear to the crankshaft again.

PICTURES: Some cool pics and more info about the gears are here.