There are two different types of deposits: Security and Holding deposits.
The security deposit is paid by the tenant when moving in. This information is stated in your listing and in the booking request and confirmation emails.
The deposit is used to cover for any potential damages that may occur during the stay or to be used as compensation in case the tenant leaves earlier than originally booked. If no damages occur, and the tenant leaves on the agreed move-out date, the deposit should be refunded to the guest in a way you both agree on.
Although the deposit is mentioned several times, it always helps to send a small reminder to your tenant before the move-in date.