One person can manage but another set of hands is helpful. A drop cloth or vacuum is handy to catch the debris you will make while drilling.
Level, Pencil, 3/16” Drill Bit, Drill/Driver
FIND A STUD in the area you would like to mount your shelf.
HOLD THE SHELF LEVEL in desired location.
MARK THE HOLES with your pencil and remove the shelf
DRILL THE HOLES.Check to make sure at least 2 of 4 holes per flange are in a stud.
RE-PLACE SHELF and INSERT SCREWS.
Make sure it is still level and make adjustments as needed.
Stand back and admire your new (old) shelf!