You will need:
Align the leg plates, and place a standoff between each of the bottom three pairs of holes in the plates. Secure each standoff to the plates with a 5 mm bolt on each end. Insert the support plate into the horizontal slots at the top of the leg.
Align the two holes in the top of the leg with the two holes in the center of the arm. Orient the leg with the point facing towards the center of the copter. Insert two 25 mm bolts through the arm and the leg, and secure with metal nuts.
Repeat these steps for each leg of your copter.