Two ways in
There is a check-in button on the home screen, and there is a Clock in for this shift button on the shift itself. They do the same thing, but the second one tells Paddl which shift you mean, which matters if your signal drops.
The button on a shift appears from an hour before it starts until four hours after. It does not appear on a shift that has already finished, or if you are already clocked in somewhere.
The location check
When you clock in, the app asks your phone where you are and sends that with the check-in. If you are within 100 metres of the site, the check-in is marked verified.
If you refuse the permission, or you are somewhere with no GPS, the check-in still goes through. It is simply recorded without a location, which your manager can see. Nothing is blocked.
No signal
Clocking in works with no connection. It is held on your phone and sent when you are back on the network, stamped with the time you actually tapped it rather than the time it eventually sent. Clocking in from the shift card is worth doing here: days later there may be nothing left for Paddl to work out which shift you meant, and the hours would end up recorded as unrostered.
Clocking out
Clock out from the home screen when you finish. If you forget, Paddl closes it for you: half an hour after your shift was due to end if it knows which shift you were on, or a couple of hours after the site closes if it does not. Either way it is flagged for your manager, because a figure the system worked out is not the same as one you recorded.
Clock out properly if you can. An automatic close is a best guess, and your manager has to check it before your hours are approved.