Place both side rails in parallel positions where you want the bed frame assembled. The side rails are the two longest rails.
Place the cross rails across the top and bottom between the two side rails. Locate the mounting holes along the rail, and position the cross rails over the mounting holes so that you can snap them together. Press the cross rails into place until they lock into the side rails.
Insert the center rail in the middle of the cross rails. The center rail attaches to the inside of the top cross rail and the inside of the bottom cross rail. Align the rail with the notches in the cross rails, pressing it into place until it locks.
Press the casters or wheels into the mounting holes on the bottom of the frame. There are caster mounts on each of the four corners of the frame. Press the safety caps into the open ends of the side rails to protect the rough, exposed edges.
Mount the headboard to the frame, if applicable. The headboard end of the frame will slide into the mounts on the headboard. Position your mattresses or box spring assembly onto the frame.