Lay the wood on top of the aluminum sheet. Trace the wood on the metal sheet. Offset sheets are also available for you to use. Most printers or newspaper companies give you offset sheets they aren't using anymore because of misprints.
Use scissors to cut the aluminum around the traced area. Leave enough space around the edges to cover the width of the wooden board.
Cut into the corners and fold the aluminum to make the corner.
Apply the glue to the metal sheet. Place the wood on the back. Press the board into the sheet. Check that the glue slicks. Glue the edges down and allow the glue to dry.
Mount the desk to the wall with metal brackets. Screw the mount onto the bottom of the desk. Mount the other side to the wall where you want the desk to be located.