Install asphalt roof shingles videos from the web.
Even though there are many instructional resources as to how to do much of the asphalt roof shingles install work by yourself, they still leave much to be desired in terms of explaining how the work is done in real life.
That is why videos about the installation process are so helpful. The videos can help you visualize and schedule the work process, and you can avoid some of the pitfalls of doing the work, such as starting the shingles install from the wrong place.
As an overview, here's a video of how shingles were installed to one garage roof after the old shingles are removed:
As for removing and replacing few shingles, Tim Carter from Ask the Builder has a great short video about what tools you need for the shingles replacement and how to do the work:
If you have damaged shingles beyond a few, it's probably a good idea to use a roofing contractor. Here's one roofing contractors viewpoint into the roofing work and the process: