The motor shield can drive up to 4 DC motors bi-directionally. That means they can be driven forwards and backwards. The speed can also be varied at 0.5% increments using the high-quality built in PWM. This means the speed is very smooth and won’t vary!. Note that the H-bridge chip is not meant for driving loads over 0.6A or that peak over 1.2A so this is for small motors.