Follow one position report from a truck on Highway 3 to the map on your phone. Change the path, switch the Internet off, and watch what still gets through on radio alone.
Swipe sideways to see the whole map.
Radio side. In North America, APRS runs on 144.390 MHz. Packets go out as 1200-baud AX.25 packets: about a second of tones per beacon, shared by everyone on the channel.
Internet side. An iGate is a station that hears packets on the air and passes them to APRS-IS, the Internet network behind maps like aprs.fi. When the same packet arrives more than once, APRS-IS keeps only one copy.
Choosing a path. More hops reach farther but tie up the channel for everyone, so use the shortest path that works where you are. Local practice varies, so ask your area's digipeater owners. This is a simplified picture: real ranges depend on terrain, antennas and power.