Click on 'Backup' and the next window will show three options via which you can extract data for backup.
Single Backup, Import CSV, and Domain Users are the three options provisioned.
If you go for ‘Single Backup’, provide your Google Apps account credentials i.e. Username and Password and click on Register.
While, if you choose 'Import CSV' option then you can import multiple users at a time. A CSV file, maintained with the credentials of the accounts from which you want to backup data must be browsed. Click on Import to proceed.
And if 'Domain Users' is chosen then you are required to provide Administrator credentials for the backup. Provide; name of the Domain, Administrator Username, Administrator Password, Consumer Key & Secret Key. Click on Register and continue.