@Praveen6, when you book, there are two types of listings, one kind is Instant Book, where a booking is automatically accepted, when you meet the criteria, and the other type is abooking request, where the host has 24 hours to accept you booking.
In such a case, the airbnb website checks with your bank, if you can pay the stay. If your bank’s computer confirms, then the form is sent and your hosts gets the request. If he says Yes, the money is taken from your card and you get a confirmation. If he says No or lets the request expire, the money is not taken.
A host should not let expire a booking, because that blocks his calendar for other guests too.
I hope you will get your confirmation soon..