Following a trail means you have some reference of a foot path to stay on and follow. Navigating could mean anything--it might be reading a vague description like "follow the trail to a cairn at mile 5, then bushwhack up hill 1500 vertical feet to a ridge, follow the ridge as it ascends the mountain choosing an obvious class 3 scramble on the east side that avoids serious exposure (if you encounter class 5 terrain you are off route)". With navigation you have to use a lot more senses and tools and knowledge, the path isn't immediately obvious.
Navigating is looking and matching up landmarks to a map to identify your current position, and then determining the route you will follow. (Orientation) From there, you use a compass to follow that route, counting your steps. You have to know how many steps it takes you to walk a km/mile, then you can reorient every so often to adjust your route based on your real position.