If you arrive at your destination to find that your luggage has been damaged or lost by the airline, immediately report it to the airline at the Baggage Claim.
You will be asked to fill in a form with the details of your suitcase and details of the damaged and missing items. And most importantly your contact details.
If your case is damaged we would recommend that you take photos. Make sure you keep any receipts provided by the baggage claim staff, incase you make an insurance claim.