Been asked thousands of times before, which you'd have found if you'd bothered to search for yourself.
In all probability it is either the flame falure thermocouple not having the pilot flame playing on it properly - soot, burned food in the way, maybe or the thermocouple has failed.
Simple enough to find spares - if you are prepared to search and simple enough to replace. There may even be videos to be found - if you are prepared to search
XXX, February 2017
