Have you never heard that term before? Just how young are you?
It's a term that means "easily" or "with little or no effort". You can find it's definition in the Oxford English Dictionary.
"'Hands down,' dates back to the mid-19th century and harks, not from card-playing or schoolyard fisticuffs, but from the genteel world of horseracing. A jockey nearing the finish line well ahead of the competition, with victory certain, would often relax his posture and drop his hands, relaxing his hold on the reins, as his steed galloped the final few yards. To win a race "hands down," therefore, was to win it easily, without any serious competition, and by the late 19th century the phrase was being used in non-racing contexts to mean 'with no trouble at all.' "
So, in otherwords, when I say that feta is the best cheese, hands down, I am saying "feta is easily the best cheese".