Sand all faces of your lumber, once with coarse grit paper and once with fine grit paper.
Apply one coat of stain to all faces of your lumber. Allow to dry.
Set one 48-inch plank and one 58-inch plank in an L, with the end of the 58-inch plank abutting the face of the 48-inch plank. Glue in place with wood glue. Allow to dry. Once dry, drive three evenly spaced finishing nails through the face of the 48-inch plank and into the middle of the edge of the 58-inch plank.
Set the second 48-inch plank against the open end of the 58-inch plank, forming a C. Glue, dry and nail as you did the first connection.
Slide the second 58-inch plank in between the 48-inch planks, parallel to and 12 inches from the other 58-inch plank. Glue, dry and nail both ends as before. This forms a headboard with a shelf at the same level as the top of your bed.
Support the middle of your shelf by attaching the 36-inch plank to the middle of the underside of the lowest 58-inch plank. This plank will run parallel to and 29 inches away from the planks on either side. Glue, dry and nail as before.
Set your lumber sheet on the frame with its edges flush with the edges of the frame. Glue and allow to dry. Once dry, drive in a finishing nail at each corner and four evenly spaced nails along the side and top edges.