Save you notes, questions, highlighted text fragments, topics, general notes to a file so that you could restore them in case you need to change your phone. Backups are created automatically every time you open application and saved to the Gitabase folder on your device.
Files are named as gitabase-reader-notes(Weekday index).db, where (Weekday index) is digit between 1 and 7.
One such file stores all your data.
You can also make a backup using command from the main menu on the library (L) screen. This command creates a backup file which can be used to restore your notes on another device.