Here's how...
Each satellite broadcasts its signal with an embedded time code. Your receiver receives and processes this time code and compares it to its internal clock. The difference in the receiver clock to the broadcast clock gives you time traveled. Assuming a constant radio wave speed, the receiver figures distance from the satellite.
Imagine this distance from the satellite. It gives you a sphere the calculated distance from the satellite. Two satellites give you two spheres. The receiver knows where each satellite is because the satellites also broadcast position data for the entire satellite constellation. The two imaginary spheres intersect on a circle (plus or minus distance error caused by inaccurate satellite and receiver clocks, orbital errors, multi-path error, etc.). Add the distance from a third satellite and you derive two possible points (the receiver can generally discard one and assumes that you are somewhere near the surface of the earth). This gives you a three-dimensional solution (which is why we call it triangularization - three satellites triangulates your 3-d position). However, as noted, the orbit and GPS clock errors make this a fuzzy solution. This error adds a fourth variable to the position equation. A fourth satellite provides the information to fully resolve your position accurately.
Several good sites on GPS that address this in more detail.
Good luck.