Cut with the table saw (or have the home improvement store cut) two lengths of the lumber to the length of the shelf you desire. You now have what this article will call the "shelf board" and the "support board".
Use the tape measure and pencil to make dots 1/2 inch from the edge and about 5 inches apart along the wide surface on the long side of the support board,
Use the drill and the drill bit recommended by the wood screw packaging to drill pilot holes where you have marked the dots in pencil.
Place the long, thin side of the shelf board against the edge of the support board with the pilot holes. The boards need to be arranged in an "L" shape with the pilot holes directly under the long, thin edge of the shelf board.
Screw the wood screws through the pilot holes and into the long, thin edge of the shelf board.
Attach two keyhole hangers to the back of the support board using the screwdriver, about 2 inches from the corners and 2 inches from each edge.
The picture shows what keyhole hangers look like so that you can find them at the hardware store.
Sand and stain or paint your project, if desired.
Hang the shelf using wall anchors, hooking the wall anchors into the picture hangers.