Set the headboard against the wall in the approximate area of the room where you want the finished bed to reside. Lay the metal rails perpendicular to the headboard. The horizontal part of the metal rail should face inward, while the vertical part is on the outside.
Hold one of the bed hook adapters up to the headboard side of one rail. Align the bolt holes on the adapter with the bolt holes on the rail.
Screw in the bedframe bolts until they are secure and the bed hook adapter doesn't wiggle. Repeat with the other adapter and rail.
Assemble the rails by connecting the cross piece and the foot piece. Extend the cross piece arms toward each other from the centers of the rail. Align the pins and push them together until they engage. Repeat with the foot piece. Lay the wooden bed slats across the rails. The rails should be standing in place now, just without a headboard attached.
Move the sleigh headboard into position, with the slot lining up with the hook part of the bed hook adapter. Insert the bed hooks into the slot and press down. The hooks will engage and hold the rails snugly to the headboard. Repeat with the other side of the headboard. Move the bed into position and add a box spring and mattress.