“Collaboration Projects” (aka Shared Projects) are Projects in which a user has been invited to another user's Project.
To add another user to your Project, click the blue [View] button associated with your Project.
In the "Add Users to Your Project" field, type the full email address of the user you'd like to invite. They will be invited to your Project. The user will then be able to interact, upload, and download files associated with that Project.