Those who fail in their bids get only one point per trick. A correct prediction earns 10 points, plus one point for each trick won. Because each player, after seeing their cards, must guess how many tricks they are going to win.
What makes oh hell! superior to most forms of whist is that you can come out on top even with a hand full of dross. The latter method has two drawbacks: one, everyone gets to see one of the cards missing from the deal, and two, no-trumps rounds are impossible (unless you agree that, for example, a picture card in any suit means no trumps). Trumps are decided either by a predetermined list (hearts, diamonds, clubs, spades, then no trumps) or by turning up the top card of the remaining pile.
The player of the highest card (or trump) wins the trick. Play proceeds as in whist: the player to dealer's left leads, and the next player follows suit or, if they can't, throws away a card, or lays a trump. Deal an equal number of cards to each player - sometimes 12 but usually seven to start.