How does one register function work?

Single Register mode is a Location management mode with a single receipt printer and a single cash drawer only. Therefore, from the moment you created your account, you used bePOS in Single Register mode. Single Register mode does not limit the number of iPad/iPhone devices used at the store. Single Register mode is also flexible and allows multiple iPad/iPhone by multiple staffs to connect to the printer and cash drawer (if granted permission). Thus, for small and medium sized stores - only one cashier counter with one printer and one cash drawer only, bePOS recommends that you keep using the default Single Register mode (Location management).

Refer to Multiple-Register Mode article here.