Hold the shelf brackets parallel to each other on the concrete wall in the desired location for the shelf.
Place a level across the top of the brackets and adjust the brackets so the shelf will be level. Mark the mounting holes in the brackets onto the concrete wall with a pencil. Set the mounting brackets aside.
Drill a hole that is 1/4 inch deeper than the length of the masonry screws, using a hammer drill and masonry bit, at each pencil mark.
Hold the brackets in place against the wall. Drive a masonry screw through each mounting hole in the bracket into the concrete wall with a screw gun to mount the brackets to the wall.