Once you've selected the space you would like to use, click Book to be taken to a page where you can review the details of your booking and select how you would like to pay.
If the space is instantly bookable, your booking will be confirmed when you click Book now. Otherwise, the status of the booking will be shown as pending until it is confirmed with the host. Hosts are required to respond within 24 hours, most reply much sooner. Payment will be charged to your account only once the booking is confirmed.
For more information on booking status, see What does the status of my booking mean?