Tablet enabled with cellular data service work in a similar way to cell/mobile phones. There is a fee to purchase the device and also a monthly fee for the cellular data service with a monthly data transfer limit. The higher your data transfer limit, the higher the monthly fee. If you exceed your monthly data transfer limit, there are overage charges which can be very expensive.
The cellular service plan for the device is billed through a carrier, in the case of StFX the carrier is Bell. Depending on the carrier, the iPad model, and your location, you may have various cellular plan options including in some cases the choice of 3G or 4G cellular data service.