When you are landing an airplane, or trying to slow it down while on the ground at any time, you will usually employ toe brakes. These are the main landing gear brakes for the craft. Toe brakes are integrally mounted pedals above the rudder pedals, one for the right foot and one for the left foot. Sometimes a plane will have only one toe brake.
To use them, depress the pedals simultaneously with your toes. You may also wish to cut back on the throttle so as not to burn up your brakes and wheels. These babies really come in handy when you want your airplane to stop.
For getting the full experience of toe brakes in a computer flight simulator(such as Microsoft Flight Simulator), I recommend using CH products Pro Pedals. The default control for toe brakes is the joystick trigger or the "." key. The pedals make for a far more realistic simulation.