To check the availability of a listing, contact the host first by clicking on “CONTACT HOST” on the listing page. This feature doesn't require you to provide any credit card information. You are encouraged to use it to be in contact with as many hosts as you want, before you decide.
If a host responds with a Pre-approval, it means that he has confirmed the availability of his place at your desired travelling dates, and you are welcomed to book within 24 hours. You can also ignore a Pre-approval without any charge.
TOP TIP: You can visit the calendar not only to check availability of the accommodation but the price as well, as it may vary from weekdays to weekends, or according to seasonality.