It needs to be place where when it is in the catch the bottom blade is behind the bottom stock and can not be seen. Next attach the pulley to the top. Put a rope cleat or screw on the outside of the upright and tie the rope to it. This will keep the top blade out of your way. You'll learn what to do with it when you build the stocks.
Next lets make our bottom and top stocks.
The bottom stocks hold all the magic illusion of this guillotine. Start by cutting 3 pieces of plywood 13 inches x 18 inches and one 27 inches x 18 inches. The larger piece is the back bottom of the stocks and runs all the way down to the cross support. Locate the middle of one 18 inch edge on each piece, and use as a center point. Tie a piece of dowel to the rope so it won't slip back through the hole.