The shoe clip anchors the bottom of your XTERN to your shoe so the brace lifts your foot with every step. You only need the parts in the clip kit and the shoe you wear with the brace.
Put the shoe on and stand up. Mark the spot on the outer side of the heel, about 20 mm above the sole, where the bottom of your brace rests.
Place the clip flat on the mark with the open side facing the back of the shoe. Both screw holes should sit on smooth material, not on a seam.
Using the small hex key from your kit, turn the front screw in until it feels snug. Do not tighten it all the way yet.
Put the brace on and slide the footplate into the clip. Pivot the clip slightly until the brace sits straight and comfortable.
Take the brace off. Put in the second screw, then tighten both screws firmly.
Put the brace and shoe on and walk a few steps. The clip should hold the brace firmly with no rattling. You are done.