1 - S Mode. Allows you to "Shift" through the gears with the lever or the paddles on the wheel. Shift if quotes because they are just fake shift points in the CVT.
2 - B Mode. Engine braking, uses the engine RPM and gearing to slow the car down, kind of like cruise control on a hill.
I believe the S mode is on the S models and the B mode is on the Le(eco?).