A) grobit uses the “Open Food Facts Database”. So items which are already in this database are automatically identified. In case your item is not found on scanning your barcode, you will be auto directed in the app to the item selection screen. Simply link the barcode to an existing item OR create a new item by typing the name and link it. With the next scan the item is automatically identified.
Note : In case you have backed up your data (or synced them) to other devices, the barcode data will be synced with it.