From the wiki
Adding a File Server
Ensure that the file server is active and connected to your network.
Quick-reload the router. In the Orbiter, click More -> Advanced options -> Quick reload router.
The orbiter will display a message identifying the detected network share, and ask what you would like to do with this share. Click File Server.
The orbiter will ask for the user name and password for this file server. If the file server does not require a login, simply click Ok.
The orbiter will inform you that the File Server has been created, and ask which room the file server is in.