To add an external storage device to OneDrive:

1. Plug in external storage device.
2. Open the OneDrive application on the device.
3. Sign in with your Microsoft account details.
4. Select the 'Settings' option.
5. Click the 'Add an external storage device' option.
6. Click to agree to the terms and conditions.
7. Enter the 'Drive Name' for your external storage device.
8. Click 'OK.'