When a dog walks, it first moves one rear leg forward, then the front foot on that same side. Then it moves the other rear foot forward, then the front foot on that side. So the pattern of footfall for the walk is right rear, right front, left rear, left front (repeat).
As a dog walks, sometimes two feet are on the ground; other times there are three. The walk is the only dog gait in which three feet can be on the ground at the same time. If you see three of your dog’s feet on the ground, you know your dog is walking.