Does the host need to approve my booking?

It depends on the space. Some book instantly; others send your request to the host first. When the host must accept, the listing's booking sheet says Request to book, and so does the checkout button. An instant booking's checkout button says Confirm and pay. If you are paying online with a new card, the button may simply say Continue.

Booking outside a space's usual hours turns it into a request, even on a space that normally books instantly.

For a request, you pay when you send it. Checkout shows when the host must answer by. If they say no or do not answer in time, you get a full refund. Your bank can take up to ten working days to show a refund.