Open it
Intercom menu → Map, or the map icon at the top of Channels.
What is on it
Green dots: APRS stations the radio decoded (any analog channel, APRS monitoring, ISS APRS), at their last position; APRS-IS stations are not shown. Cyan diamonds: FM repeaters; violet diamonds: DMR repeaters, within the Nearby repeaters range (15 to 120 miles). Amber pins: your channels that have a location (channel editor → Location). Blue dot: you, moving with the phone while the map is open; the soft circle around it is how accurate the fix is.
Moving around
Drag to move, pinch or double-tap to zoom. The buttons on the right zoom in and out, go back to your position, fit everything on screen, and (the last one) show the repeaters around the middle of the map: move the map anywhere, tap it, and the repeaters within your Nearby repeaters range of that spot replace those around you. The pills at the top hide or show each kind: APRS (the stations received), Repeaters and Channels; the number is how many there are. The map remembers which ones you turned off.
Markers
Tap one for a card: a station shows when it was heard, its path, speed, altitude and comment; a repeater shows its frequencies and tone and opens its details to add it as a channel; a channel can be used straight away. Every card can open the place in your maps app.
Coverage
The violet Coverage pill adds your measured coverage: where each repeater was heard and where your transmissions keyed it. See Coverage maps.
Map tiles
From OpenStreetMap (© OpenStreetMap contributors), darkened to match the app and kept on the phone for 30 days, so places you have looked at still show offline.