Each zone has different unlock requirements, which must be filled in order to unlock it. The zones don't have to be unlocked in order, but you can only scout in the current zone and locations that have a connection to your current location, so even if you unlocked a distant zone, it remains unaccessible unless another character leads you there.
Scouting reveals locations in a random order. It's possible to fail at scouting if you're unlucky. Then the chances of finding a location are increased for subsequent attempts.
Scouting reveals the travel requirements for a particular location. Once you have filled the travel requirements, you can travel to that location. The first time you travel to a location, exploration AP is added to the cost. After that, you can travel to it at any time as long as you continue to have the required equipment.
If you are for example at a swamp and someone steals your wading boots, you can still travel away from there even without filling the requirements because it only checks the requirements for
moving to a location, not
moving away from it, but you can't go back unless you acquire new equipment. The exception is islands, which now require a boat or a raft to leave. This was changed to make it impossible to accidentally walk away from an island and leave your boat behind. If you are marooned on an island, you can always get wood through the random finds icons and eventually construct a raft, which is cheaper than a boat.