RockShox Motion Control is a high-tech damping system that's easy to adjust on the trail.
1) Compression Adjustment (blue knob in photo): You can adjust the amount of suspension movement you get from a hit with the compression adjustment. As you turn the knob clockwise from the wide-open to the closed setting, it takes more speed and pressure to move the suspension. Keeping the compression adjustment in a closed or close-to-closed position prevents the fork from moving or reacting to slow-speed inputs, such as brake dive or bobbing caused by pedaling. Note that the compression adjustment doesn't change the fork travel at all.
2) Floodgate: The Floodgate is essentially a blow-off or bypass valve for the compression adjustment when the compression adjustment is in the closed or close-to-closed position. If you hit a large bump, the floodgate overrides the compression setting and the fork moves freely.
Setting Suggestions: For super-smooth trails, roads and getting the holeshot, turn the compression all the way to the closed position. For cross-country racing and fast riding, loosen the compression just a bit to get a smoother ride. For rough, technical trails and anytime you want a plush ride, go with medium to low compression for maximum fork movement (the floodgate only affects fork movement at high compression rates).