In a multiuser environment, the user who creates a workspace resource (a project or a Code Search list, for example) is referred to as its owner. Only the owner can share the resource with other users.
A shared, or public, resource is visible to other members of your team. A private resource is not. If a public resource is protected, team members can view but not edit or delete the resource. A Code Search list, for example, is always protected.
You can turn sharing on and off in the tool you use to create the resource. Look for a symbol like this one for a shared project to indicate that the resource is shared.