Measure the wall to determine the available space for the file shelves.
Cut sections of 1-by-12-inch lumber to the desired shelf width with a jigsaw.
Locate the wall studs with a stud finder. Mark the location of the studs with a pencil.
Place one of the file shelves against the wall. Place a carpenter's level on the shelf and adjust the shelf until it is level. Draw a pencil line on the wall along the bottom of the shelf.
Attach shelf brackets on the wall on each stud with 4-inch wood screws and an electric screwdriver, using the shelf line as a guide.
Place a shelf on the metal brackets. Secure the shelf to the brackets with 3/4-inch wood screws. Repeat this process for each shelf.