Breaststroke kick is probably the hardest part of the stroke. It is also the main part of the stroke, where the majority of the power comes from. Most breaststrokers have extremely flexible ankles and hips, as your feet bend in different ways than performed in the other three strokes.
For the kick, your feet should be flexed unless they are being kicked together, then they are pointed. Your knees should also not go outside your shoulders, and they remain very close together.
One of the best ways to practice your kick is to grab onto the wall and extend your body on top of the water. Holding onto the wall, practice your kick. Your feet should not be coming out of the water and if they are, trying lowering your hips a bit, but they should still be flat with your shoulders. Your feet should also not come above your rear when they come around.
I am not the best breaststroker, so I have provided a link to breaststroke kick drills, which can be found here.