OK, so the easiest examples are when you’ve got internal spaces, broken up into rooms and corridors. The room you’re in, that’s one zone, unless the room’s really big (in which case, it might be split into a couple of zones). The corridor outside, that’s the next zone. A room off that corridor, that’s another zone. That’s a simple three-zone map - each zone is a distinct area on that map, and any character involved in that scene will be in one of those three places, and describing position and movement is literally as simple as mentioning the room the character is in and where they’re going.
All you really need to track is which zone everyone is in. Which is, when you think about it, less exacting than having to determine that your Ranger is 30ft from that goblin, 15ft from the group’s Cleric, 60ft from that Troll, etc. Those things are all easy to do if you’ve got miniatures and/or maps, but tend to be abstracted into “eh, close enough” when you’re trying to do them in your head, in my experience.
The zones are fixed places on the map, but range is relative to the person - what counts as close/medium/long range depends on where you are at the time, obviously. Anyone in the same zone as you at that time, is in Close range. Anyone in a zone adjacent to your current zone is in Medium range. Anyone two zones away from you is at Long range. Anyone three or more zones away is at Extreme range.
If you use a Minor Action to move, you can move to anywhere within Medium range, so you can move to anywhere within your current zone or any adjacent zone. Essentially, you’ve got a movement of 1: you can move up to one zone in any direction. Next turn, you’re in a different zone, so what counts as Medium range is different to what it was last turn.
So, back to the example above. You choose to move, and you can move into the corridor outside. Next turn, a minor action move would let you move into either room, because both rooms are adjacent to the corridor.
Hope that helps.