Lean the headboard against a wall in the area of the room you want to keep the bed. Hold the headboard so it's standing upright, and slip one of the bed rails into the slot near the bottom of the headboard's left or right leg.
Push the rail into the headboard as far as it will go. Use a hammer to lightly tap the rail to make sure it's in tight. The rail shouldn't move if it's the proper fit. Repeat this process with the other bed rail.
Hold the footboard upright and slip the other side of each of the bed rails into the slots at the bottom legs of the footboard. Push the footboard into the rails as far as it will go. If the bed has metal slats between the rails, the bed construction is complete.
Place the spring frame onto the bed rails if there are no metal slats. Place the mattress on top of the springs.