The brake + front wheel lock are designed to make the stroller easy to steer and stop.
To use the brake:
Push down on the bottom of the pedal to prop it upward and lock the brake in position.
If you want to release the brake, flick the pedal back up to a level position.
To use the front wheel lock:
Pull up the lever located on the right side of the frame to activate the lock. This will lock your wheels in a straight forward position so that they cannot turn.
If you want your wheels to turn, simply push down on the same lever.