All it does is record where you've been, max speed, current speed, average, time, distance, stores waypoints, etc. the yellow one doesn't have any road maps, but I use mine for camping, cycling, and hiking, not for navigation to unfamiliar places.

The vista models do have maps/navigation.

The yellow one, when it has a good view of the sky is accurate to 12 feet or so. The vistas have WAAS, which is a terrestrial accuracy augmentation signal based on land transmitters, and they can be even more accurate.