Raise the beam clamp's support screw so that the distance between the bottom of the screw and the beam's bottom jaw exceeds the height of the beam to which you'd like to attach the clamp. Turn the screw counter-clockwise to raise it.
Place the mouth of the beam clamp over the area of the beam where you will attach the clamp. Push the inside of the beam clamp's bottom jaw up the bottom of the beam and hold the clamp in place.
Tighten the support screw so that it secures the clamp to the beam. Turn the screw clockwise to tighten the beam clamp securely to the beam.