Align the loose shingle with the adjacent, installed shingle. Load a roofing nail gun with roofing nails or hold a single roofing nail in one hand and a hammer in the other. If using a nail gun, use one hand to stabilize the shingle's position. If using a hammer, stabilize the shingle's position with the butt of the palm of your hand that is holding the nail; using the butt of your palm keeps your fingers and hand free to position the nail.
Position the nail or nail gun 1 inch from the end of the shingle that butts against the adjacent shingle; in other words, on a horizontal plane, 1 inch inward from the shingle's "side." Align the nail or nail gun approximately halfway between the shingle's adhesive strip and the end of the tab's cut-out; cut-out refers to the slit that runs from the shingle's bottom edge to approximately the center of the shingle.
Drive the nail through the shingle and into the sheathing with a nail gun or hammer the nail with a hammer. If using a nail gun, align the gun perpendicular to the roof's surface so the nail drives straight. If using a hammer, use deliberate, forceful blows to ensure that the nail drives straight. Pound the nail until the nail's head rests flush with the shingle's surface.
Place the second nail above the tab cut-out closest to the first nail and halfway between the cut-out and the shingle's adhesive strip. To proceed with a four-nail installation, leave the nail in this position, drive the straight through the shingle and flush with shingle's surface. For a six-nail, high-wind installation, move the nail approximately 1 inch to the left of the cut-out and drive the nail. If performing a six-nail installation, place a nail approximately 1 inch to the right of the cut-out and drive the nail.
Set a nail above the remaining tab cut-out and position the nail halfway between the cut-out's top and the shingle's adhesive strip. If you are performing a four-nail installation, drive the nail through the shingle. If you are performing a six-nail installation, drive a nail one inch to either side of the cut-out slit.
Align a final nail at the loose end of the shingle, 1 inch inward from the edge and halfway between the end of the cut-out slits and the adhesive strip. Drive the nail through the shingle with a nail gun or hammer.