Purchase as many shelf tops as you want to install. If you can’t cut them yourself, the lumber yard can cut them to your specifications. Generally for single shelves, or columns of shelves, 12-by-36 inches is plenty.
Mark a level line, or lines, on the wall where you want to put up the shelves. Use a stud finder to mark out the stud locations on the line or lines. You want three adjacent studs for each shelf.
Place a decorative shelf bracket on each of the stud points and secure it the wall and the stud underneath with 2-inch screws through each of the screw holes in the shelf bracket.
Center a shelf top over the three brackets. You can leave the shelf removable or fasten it to the horizontal bracket arm with 1/2-inch screws through the screw holes in the bracket into the underside of the shelf top.