@Debbie-And-Jenny0 The guest will need to pay at least half of the cost of the booking at the time the accomodation is booked; it depends on if the guest is elligible to pay less upfront. The reservation isn't comfirmed until the payment is made.
See the terms of Pay Less Upfront here:
https://www.airbnb.ca/help/article/1696/pay-less-upfront-terms
General info on when guests are charged for a reservation are here. This article doesn't include details on the Pay Less Upfront feature:
https://www.airbnb.ca/help/article/92/when-am-i-charged-for-a-reservation
The guest will have sorted all of this out before they book with you, because the system tells them everything they need to know about when payment is collected. I have never gotten a question from a guest regarding payment: it's all between them and Airbnb.