The majority of horses in the world have four natural gaits: the walk, the trot, the canter and the gallop (some would classify the gallop as a fast canter, but because the sequence of footfalls goes from 3 to 4 beat, many consider it a separate gait). There are other gaits beyond these four that are a result of special training or specific breeding.
The walk, the simplest and easiest to recognize of the gaits, is a four beat gait. By four beat we mean that each foot hits the round in succession. If one were to listen to the horse walking on a hard surface, for instance concrete, you would hear a distinct 1-2-3-4 pattern as the horse walked. When a horse walks one foot is lifted off the ground at a time, the other three remaining on the ground. The sequence of the footfalls is left front, right hind, right front, left hind.
The trot is a two beat gait where the legs are moved in diagonal pairs, i.e. the left fore and right hind are off the ground and moving while the right fore and left hind