Decide how high you wish to hang the handrail. From the stair treads to the handrail's surface must be between 34 and 38 inches. Mark this height on the wall in two locations.
Set up a laser level at the bottom of the stairs. Aim the laser level up the stairs and line it up with the two marks you made. Run a stud finder along the wall, over the laser line, to locate the wall studs. Mark each stud you come across.
Measure the handrail's thickness. Select a wall stud near both the top and bottom stair treads, as well as one in the center of the staircase if there are 14 steps or more. Measure down from the laser line the handrail's thickness on each selected wall stud and make a mark.
Line up a fitting's top edge on one of the marks you made in the previous step. Hold a torpedo level against the fitting and adjust it until it is plumb. Drill 1/8-inch pilot holes through each of the fitting's screw holes, then secure it to the wall stud with the provided screw. Repeat this step for each of the fittings.
Set the handrail on the fittings. Extend the handrail's bottom end slightly past the bottom tread's nose. Ask someone to hold the handrail in place.
Place one of the supplied fitting collars under the bracket with the two tabs pressed against the handrail's underside. Drill 1/8-inch pilot holes through each of the collar's screw holes, then drive the supplied screws through them to hold the collar in place. Repeat with the remaining brackets.