And once displayed, does anything else have to be done to start navigating with it?
To clarify - on the E30, to start navigating (ie with prompts) - and the ONLY way to start navigating - you go via the "Where To?" button. (You don't need to do anything else, eg set to display on map etc - just this.)
This gives a submenu to choose between Waypoints (if available), Tracks (if available), Routes (if available), Map Points of Interest (eg stations, hospitals, restaurants etc) if available, User POIs if available. Or you have an option to just point to somewhere on the map.
Availability of the first three depends on any GPX files that have been loaded into the GPS, availability of the Map Points obviously depends on the map installed. (User POIS are as they say beyond the scope of this article.)
Choose any available item from these lists and then choose 'Go' to start navigating. Simple and quick.
What happens next rather depends on your setup. If you don't have a routable map installed, you will go straight into navigation mode, with an onscreen straight line to the point, or the start (or nearest point) of the Track or Route, that you have selected. A Track, or a Route (in direct mode, the only option in this case) will work - sort of - even without a map.
If you do have a routable map installed, it will either go straight into navigation mode but this time a wiggly line following the roads, or - it will prompt you to choose one of three methods of navigation, like this:
IMO it is greatly preferable to see this prompt and have this choice, and this is a setup thing - in Setup, Routing:
Tip: if you're having difficulty seeing your Track or Route GPX in the GPS, try loading it onto the SD card, not direct onto the GPS. Same directory structure exactly, so [card]\Garmin\GPX\ . Maybe it's just me, but I find this is more reliable. You will find your tracks etc are rather 'sticky' though! If you delete everything off the card - you'll find your old tracks and routes and waypoints are still there! (Because they are cached in GPS memory.) Very annoying. You have to delete them via the GPS menus as well.