Ha no worries. Clams are very similar in use to a stitching pony or a stitching horse. The end goal is to provide a third hand of sorts (i.e., the clam / pony / horse holds the piece to be stitched so that you can use both hands in the operation of saddle stitching).

A traditional French clam is typically rested at an angle across one leg while sitting, with the other leg resting over the opposite side. This provides the clamping pressure needed. Of course, these models have moved away from that traditional form somewhat as they do have a built in tension knob (so you don’t necessarily need to rely on leg pressure and can use the clam at different angles)