1) Goto the Home screen (long press on any navigation bar or tap on the house icon).
2) From the Home screen slide to the right or select the icon in the upper left to activate the Home screen left menu.
3) From the home screen left menu select 'Backups'.
4) On the Backups screen select the "+" icon or pull down from the top. You will be prompted to link RetainIt to Dropbox and login on the first backup.
To restore from a previous backup just swipe the backup to the left and select "Restore". It's a good idea to remove old backups to save space on Dropbox.