If your horse has a club foot, the normal side will be big and rounded and the club side will be sloping and weak looking. The horse stands with the club foot back and the normal foot out in front while grazing. The horse leads with the normal foot most of the time. The horse has a history of stumbling on the club side. As for what causes club feet, I think it is mostly an inherited imbalance.
Nature tries to make the short side longer by growing a longer heel on that side.
Most veterinarians think that cutting tendons and ligaments will help the problem. I have seen many a horse that still had a club foot after being cut. A club foot is a whole-horse problem, not just a hoof problem. I have had good results treating club-footed horses. I try to make the toe and heel of club hoof longer than the other front hoof.