GPS is a system for determining your position in the world, usually in latitude and longitude.

Navigation is pathfinding in the real world + directions. GPS is useful (But far from the only) system for determining where you are. Navigation is often implemented as a route from point A (in lat, lng) to point B (in lat, lng) and then running an algorithm (such as dijkstra, or A*, but usually something far more advanced) from A to B. The algorithm runs on a routing graph of some kind, produced from processing real world map data.

All that a GPS device gives you is your coordinates (latitude and longitude). It does not tell you whether these coordinates correspond to a street address (you need a map for that). It does not tell you how to move between two points (you need a pretty complicated set of routing algorithms and historical/real-time traffic congestion data to do that).