The satellite signals its coordinates and time stamp to the receiver, which 
is enough information to determine the distance from the satellite to the 
receiver.  When this is done with 3 satellites, the location of the receiver 
can be found with a little math.  This math is propounded at the web page,

http://mypeoplepc.com/members/jon8338/roots_to_polynomials_and_power_series/id2.html