The Data Store API was created to allow multiple Firefox OS apps, with potentially different data structures and storage mechanisms, to create, maintain and share the same data objects efficiently between one another. Each app can then import the data into its own local IndexedDB to index according to their specific query needs. This is not necessary however, and you can just write directly to the Data Store API data store.
The available() method is used to check whether the storage area is available; this is an asynchronous operation that returns a DOMRequest object that will receive a callback when the operation is complete.