Pointing your toes inward makes the wheels roll at a slight angle which creates more friction than if they were pointing straight forward. This is where the stopping power comes from.
How much you bend your knees can be affected by your height, such that taller people may want to bend their knees a little more for better balance.
Shift the majority of your weight onto your front foot. This may feel a little awkward at first and it takes good control of your balance, so practice this part a lot. Keeping weight off of your back foot prepares you to move it while performing the stop.
The movement of lifting the foot, turning the foot, and setting the foot back down should be done as quickly and smoothly as you can. The goal is to have the three motions turn into one smooth motion. Remember that since your legs are scissored and your foot is pointing sideways that it will come down onto the ground at a slight angle towards the rest of your body. Your front leg skate will be straight up but your back skate will be at an angle.
