You need to pay attention to your "momentum" on the right hand side. You build momentum by moving in a straight line, and you lose it when you collide or if you reverse direction. When you end your normal movement, if you have any momentum built up, it is converted into bonus movement. Those bonus moves can only be used to keep moving in a straight line or they're lost. If you hit an enemy with a lot of momentum, you deal bonus damage and activate special abilities once you unlock those.