Answer:
The military "at ease" stance is achieved by separating the legs, stepping sideways with one leg to create an upside-down "V" shape of the legs. Technically, the thigh cannot move sideways (lateral), but the whole leg and foot moves sideways. The feet are set at approximately a shoulder-width apart.
The hands are placed behind the back. The back of one hand rests against the lower waist, and the 2nd hand clasps over the 1st hand. The shoulders and upper back are erect but relaxed. The military person still keeps eyes forward and maintains a respectful attention to the superior military person.