Put the shelf board upside down on the working surface. Set the brackets on top of the shelf board, and arrange them so they are evenly spaced, with one surface against the shelf board and the other surface flush with the rear of the shelf board. Mark the position of the bracket holes on the shelf board, and remove the brackets.
Drill a hole into each marking using a drill bit with a slightly smaller diameter than the wood screws you will be using to attach the brackets and making sure that the drill bit does not puncture through the surface of the shelf board. Attach the brackets to the shelf board using 1/2-inch wood screws and tightening them firmly.
Hold the assembled shelf up against the wall with the help of an assistant. Place the carpenter's level on top of the shelf, and adjust the positioning until the carpenter's level shows a level installation angle. Mark the spot where each screw will be attached through the bracket, and remove the shelf. Use the hammer drill on the hammer-drill setting and a masonry drill bit of the size recommended for your masonry screws. Drill a hole 3 inches into each marking in the wall.
Position the shelf against the wall, and use the hammer-drill setting of the drill to firmly drill each masonry screw into the wall, attaching all screws partway before tightening them all completely.