The Basic Edition of DivisiBill is free and does not show ads. It is possible to purchase a couple of additional features on the Licenses page which you reach from the Settings page, licenses are optional; the app works without them. You can use the Licenses page to subscribe to the Professional Edition, purchase a perpetual license for the Professional Edition, or purchase packages of OCR scans (for more details on OCR, see below).
The Professional Edition enables automated cloud storage and backup for bills, venue lists, people lists, and selected program properties. As an alternative to the Professional Edition, you can use the archive and restore buttons on the Manage Data page to back these things up or restore them. Alternatively, you can rely on Android AutoBackup. The subscription renews automatically unless you elect not to renew it; you can cancel at any time but there are no refunds for unused time. The perpetual license is, well, perpetual, you buy it once.
The Settings page for the Professional Edition has some additional options in order to support automated cloud backup. In practice most users can rely on Android AutoBackup to store copies of all DivisiBill data stored on an Android device in their Google Drive account, but the Professional Edition subscription provides additional control and security (files stored in the cloud may optionally be encrypted with a password of your choice).
OCR stands for Optical Character Recognition. In DivisiBill it is used by a cloud-based service to scan a picture of a bill into item names, amounts, and a few other useful values (tax, for example). It cannot help you distribute the cost of items - only you know who the participants were and what each one had - but it can take a lot of the tedium out of the item data entry process as well as making it less error prone.
Each OCR scan costs a few US cents. You can purchase packages of OCR scans in both Pro and Basic Edition. You will retain any OCR credits through an upgrade or if you uninstall and reinstall DivisiBill on the same or a different device. You can use the same account on multiple devices, and each device will decrement your remaining OCR scan count when you perform a scan from it.
Modern mobile phones can take very high resolution pictures, which are unnecessarily large and detailed for OCR. DivisiBill reduces the resolution and converts the images to black and white to save storage space and analysis time. These image files will be saved along with all the other device state by Android AutoBackup and can optionally be saved to the cloud if you have a Pro license.