Applying asphalt roof shingle is easy to do for repairing one or few shingles, but the whole roof installation is best left to professionals.
There are many resources that help you do simple installations on the asphalt shingle roofs, armed with replacement shingles, hammer, and nails.
Since seeing how the repairs are done is one of the best ways to learn, Youtube is an irreplaceable website for finding such educational resources.
One of the best such videos is from Tim Carter from askthebuilder.com:
There are some videos also available on how the work crews assemble whole asphalt shingle roofs.
Researching Youtube, one such video is available from Texas, with which you may get the idea of how the whole installation is done:
From Applying asphalt roof shingle page to Asphalt Guide index