There are two navigation app styles: map-based or cue-sheet based.
These apps show the route as a line drawn over a "base" map. Your location is indicated in some way. There may be options for auto-zooming and panning the map to show more or less detail, options for orienting the map to have North or direction-of-travel up, etc. Examples are GoogleMaps, HereWeGo, Ride with GPS, Strava, or bikemap.net. GoogleMaps and the HereWeGo app don't allow you to upload or create a route to follow. They will auto-route to the destination by trying to follow bike paths or using other criteria like the shortest distance or fastest time.
Cue-sheet based Navigation
This can be a paper cue-sheet clipped to the handlebars, or the CycleBike app on an Android phone mounted to the handlebars or stem. The CycleBike app advantages are an auto-scrolling cue-sheet display, large text size, display of current distance and direction to the next turn.
Safety: You shouldn't have to take your hands off the handlebars to navigate. For example: do you have to zoom or pan the map display to see the details of the next turn? Do you have to turn the cue-sheet over to continue navigating? Do you have to take your eyes off the road to analyze all the information on a map display?
The CycleBike app is auto-scrolling so the next turn is always at the top of the list. The text is large and the information you need to navigate is very simple. A quick glance at the phone is all that you need.
Cost: Some of the map-based apps require a data connection or a premium membership. CycleBike is free and the Route is downloaded to your phone. All you need is the GPS receiver in your phone.
Learning Curve: It may take some practice to efficiently use a navigation app. Create a route in a quiet neighborhood and practice following the route using your Android phone. Try going off-route and then navigating back to the route.