Housing is available to all players and not instanced nor phased. Housing ranges from free inn room rentals from other player to private low- to high-cost on which players have to pay taxes if they don't own tax-free deeds. The latter were available to those players that donated to the funding effort at specific donation levels.
To own a home one needs to claim a lot with a deed.
If you can't afford a deed or lot or house you can always consider renting from other player.
Homes can be within public/NPC towns or player owned towns (POTs). The towns can be accessible from the Overland Map or can be nested within other towns. The latter are always POTs and can be subterrain/cave towns too.
For those visible on the overland map you can see if other players are in the town if they have smoke coming from the chimneys and lights on in the windows.