There will be a hub area where you'll frequently return during the story, also you can return there any time using a portal to rest, restock and talk with NPCs.
There you'd be able to build a base (If you want) using materials you can gather all around the open world.
However, if you DO build there, after a while, hostile forces will take notice.
They will try to eradicate your base, and you'll be alerted wherever you are, so you can teleport home to help fight them off.
These encounters only spawn and harass you, if you decide to build. It is optional, but can offer extra bonuses to help you on your journey.