Permissions and roles
Users have different abilities depending on the role they have in a particular group or project. If a user is both in a project’s group and the project itself, the highest role is used.
On public and internal projects, the Guest role (not to be confused with Guest user) is not enforced.
When a member leaves a team’s project, all the assigned issues and merge requests are automatically unassigned.
To add or import a user, you can follow the project members documentation.