There is plenty of additional information about the GPS on the WWW. In fact, you may easily lose yourself among the many sites which cater to a broad public at many different levels of complexity.
Before you start exploring on your own hand, you may like to have a look at the sites below. Most of them have very useful onward links:
Try to search for other GPS sites on the WWW. If you do not know how to start such a search, have a look at the explanations, that were provided to participants in the Astronomy On-Line programme.