Arrange your participants in rows to form the rectangle. Have equal numbers in each line.
Call them to attention (upright posture) and have the members of each row except the first create an arm's length distance between themselves and the person in front of them.
Designate to which side the formation will dress to, either right or left. The participants on the very end of each row of that designated side stay put.
Tighten up the formation by instructing the rest of the participants to move towards the designated side until everyone is shoulder to shoulder. Now the rows are all tightened and are also an equal distance apart.
Wheel the formation in unison. This is done by having everyone involved pivot on the same heel and, naturally, in the same direction.
Move the formation at a cadence. The classic is left, left, left, right, left. This keeps everyone marching at the same pace and in tune to the movements of their compatriots.