Lay the 2-by-4-inch lumber on a flat surface. Measure and mark four equal sections that are 36 inches long, and 48-inch-long section.
Cut the lumber along the marked lines with a miter saw. Make sure the cuts are as straight as possible.
Insert two 36-inch leg sections into the 2by-4 receivers in the bottom of the bracket. Secure the wood to the bracket by hammering nails through the holes in the side. Repeat this process to attach the other two 36-inch sections to the other bracket.
Push both bottom legs together to open the bracket up on top. Insert the 48-inch piece of wood between the opening and spread the legs, bringing the brackets teeth into the wood. Repeat this step to install the other set of legs on the opposite side of the 48-inch lumber.