An instant shift, or instant booking, is a shift that you can be booked into or confirmed for without requiring the prior approval from a facility manager.
An instant shift will have a yellow lightning bolt symbol displayed on the shift card.
So if you've worked at least one uPaged shift at that organisation and you select apply and then confirm, you will be booked for the shift immediately.
If you have not worked a uPaged shift there yet and you select apply and your application will follow the normal process of requiring review by a facility manager before being accepted or declined.