The fuse box on a Lincoln Navigator contains the fuses to the electrical components on the vehicle. Depending on the year of the vehicle, there may be more than one fuse box. The year of the vehicle also dictates the exact location of the fuse box.
Fuses are responsible for things like the lights in the vehicle, the high beams, the heated seats and power seats and things like power windows and the radio. If a fuse blows, the component it works with generally stops working completely. When replacing a fuse, make sure to look at all associated fuses, because more than one may be bad and require replacing to ensure the component works without issue.