You have the option to manage all Spaces you have created and either use them on your own or share them with others. Each Space you have created is Private by default, but once you Share it with anyone it becomes shared.
You can convert a Private Space into a Shared one, simply by inviting other team members, which automatically allows everyone to collaborate on all Templates available within that specific Space:
Once you have shared access to the Private Space, it will automatically move underneath Shared Spaces in the left-hand sidebar:
Can I share a Private Space without any templates added to it?
Sharing an empty Private Space will not impact the visibility of the Shared Space. All teammates the space is shared with, disregarding the access level to the space they have, will be able to see and access it.