By default, all of your projects are private and only visible to you. However, you can create a team to easily share projects with the same group of people, whether it's your team, your organization, or a classroom.
You can transfer ownership of a project from Personal space to Team space n the project list page.
There are four access levels for team members:
Viewer - View all projects and members of a team. They can leave comments in projects, but can't change anything.
Viewers can Duplicate a project to their personal space to make changes, or request additional access. Note that when duplicating a project from a team to the user's personal space, custom environments and integrations are not preserved, and vice versa.
User - Execute all notebooks within the team and change input cell values.
Member - Create and edit team projects. Members can also connect or disconnect team integrations from projects, but can't edit or create them.
Admin - All access rights, plus the ability to manage team members and team integrations.
The Team access levels complement the Sharing settings of individual projects.
How to prevent some members from seeing one of the team projects (projects owned by the team)?
That's what private projects are for. To create such a project, navigate to "Private projects" section in the sidebar (within the team), and click on "New private project" button. Keep in mind that private projects are still using team's computational resources. You can add collaborators to the project the same way as you would to any other project. It is also possible to make the existing private project available to the whole team and vice versa by updating sharing settings of the project. Note that only team members and admins can create private projects.
How to make a project visible for the whole team, but not allow any editing?
You can enforce e.g. View-only permissions in the Manage collaborators modal for a project. This means that all members of a team, except Admins will follow the given permissions (Admins will always be able to edit all projects). If the option is set to "Full access" then all members of a team will follow their respective roles (e.g. team Users will only be able to execute notebook and change input values).