Once you arrive at the hotel you will need to check-in. The reception staff will check your identity and booking details and will hand over the room keys.
Likewise, at the end of your stay you'll have to check-out, which involves returning the keys and paying any taxes, duties or extra services used during your stay.
Check-in and check-out times vary from accommodation to accommodation; you can check them by consulting the details of your booking in the Documents in the "Purchased trips" section of your Private Area.