Never saw those when I did mine, and I'm having a bit of trouble seeing how they work as well.
The only thing I can imagine is as follows.
Put the clip with edge A on the edge of the I-beam top section, seated against the Masonite center piece. Edge B sits on the plywood and forms a U against the plywood. The screw goes through hole C and holds this in place, clamping the I-Beam to the plywood.