Cut several shingles length-wise into thirds. Each third should have a tab. In order to cut the shingles, turn them over and use a utility knife to cut along the edge where you want to make the cut. Move the piece of the shingle back and forth until it separates cleanly.
Place the shingle with the tab facing outward at the edge of the ridge of the roof peak. Bend the shingle to make it fit tightly on the peak.
Hammer two nails into the top edge of the shingle. Repeat this process to cover one side of the of the peak of the roof and then do the same on the other side of the peak of the roof.