Towns are marked by a stone ground, it is in these stone ground that you can put Placeables. As such you need to be in a town to use a Workbench or a Forge to craft certain items. per each world there are 3 towns (not verified) including the first one.
When you start playing, the Hero begins with his Robot summoned in a Town at the left corner of the world with a Cabin already placed in it. The First Town is the only town that begins with a Cabin, a Cabin can be made using 4 Wood Blocks.