In Workspace, data is organized by Project. Requirements, Defects, Tests, any of the data generated by Workspace apps resides in a project.
Once a Project is created, there are a variety of configuration options available for that Project. Access privileges or Roles may be created, Custom Fields and Alerts configured, and specific users may be added to the Project. The Project object itself may also have meta-data customized on a Project-by-Project basis, or across all Projects in an account.
Project data is generated within any of the Workspace Apps. Users first choose an app such as Agile or Defects, and then a project for recording information.