Try this:
https://www.trimble.com/gps_tutorial/
Or
http://www.edu-observatory.org/gps/gps_books.html
They should "point you in the right direction" heh...
I'd also look around for books on navigation in general. GPS is just a way of getting coordinate location, ie your latitude and longitude (or other grid-based location). Not much different than using a sextant on the high seas, really. Basically using math to triangulate your position from known locations. Once you learn about how lat/long and such works, then all the info behind the GPS system makes sense. It all starts with just getting a fix, but unlike say Cap'n Cook your electronic device can get positions so quickly and frequently and accurately that it can trace a very accurate path using all those little breadcrumbs, and then display them on electronic maps really quickly as well.
My local REI also ran some free navigation classes, so check that out. I would imagine most any navigation class these days would teach about GPS in addition to map reading, compass use, etc.
Rob
