Virtually every interesting application deals with data, and very often you want that data to survive your session with the app, so that you can return to it next time. 
To accomplish this, you must write your data somewhere, and with mobile apps you have a number of options. For small amounts of data you may well decide to write to the file system (yes, there is one!)
But for larger amounts of data, a database is very convenient, and happily SQLite comes preinstalled on iOS and Android.
Even better, nearly all the code you write for SQLite is shareable across platforms; the only platform-specific code is configuring the db connection and setting the location of the db file.
Continued here
