A public space is a place where you can write down your project you want to share with anyone . It will be indexed by search engines (or not: see the unlisted feature) so everyone can read it. You still have control over who can edit your content (including seeing your drafts).
A private space is a project that only you and the team members you invited to collaborate can access. That means it can only be read and edited by members of your organization. This is a more secure way to keep your content private to a specific group of people.
Team members can be invited to a private space via an invite link or a shareable link which is a secret link allowing non-team GitBook users (customers or partners) to access your private content in read mode only.
Learn more about shareable link :
You can choose your space's visibility when creating one, but don't worry you can change this any time, and it's very easy!
Unlisted spaces won't be indexed by search engines such as Google. They will still be accessible to anyone who links to your documentation. It lets you easily share your work-in-progress without being searchable.