Starting the first row. Basically … If you are putting new shingles over existing make sure there is only one layer of shingles already on the roof. You can add a second coat, but not a third layer. The combined weight of multiple layers is likely to be too much for the frame to handle. If you already have two layers of shingles on your house, all the shingles and tar paper below should be removed first. Then new tar paper is established, and new shingles applied over that. Always start at the bottom edge of the cover. Both the base layer of tar paper and shingles are placed with the next course overlapping the top of the previous course. Although the work is primarily physical, is not simple. Care must be taken to keep the lines parallel tiles and even the street or from any errors will be evident. See the links below for detailed instructions. I found all these links by searching "how to put the tiles."