How does GPS work?
Garmin GPS Guide for Beginners & Using Garmin GPS with paper maps (PDF’s).
http://www.garmin.com/aboutGPS/manual.html
GPS tutorial;
http://www.trimble.com/gps/index.html
Understanding GPS, map reading & survival
http://www.gpsnavmag.com/gps_navigation_training/gps_training_education.htm