they work like a sat nav, it shows a map, you input your destination, it shows you the route, then as you drive the arrow shows where you are on the road, and a voice says "exit at the next junction" etc
https://www.waze.com/en-GB/
it's like the software your sat-nav has, but running on your phone. I think the advantage of an actual sat nav is potentially bigger screen, but that's probably it.