Adding statuses is part of workflow.
To add a status:
- Go to User Menu | Settings | System Lists | Workflow.
- Click '+ New Status' beneath the list of available statuses.
- Type a name for the new status.
- Select a type for the status: Treat as Open, Treat as Completed, or Treat as Hold.
- Select what items the status should apply to: Portfolio, Project, task, Issue, Request, or a combination of these.