"Jam" is a game where everyone is trying to flick their dice to get them down the hole in the middle. When one player has got all their dice into the hole, everyone scores points for the uppermost faces of any dice they have still in play (any not used yet or knocked off the sides count as a 4). Lowest aggregate score after 1 round per player wins.
"Sumo" is a game where you start with all your dice on the board and try to flick your opponents' dice off the board (or down the hole). When someone has all their dice knocked off, everyone scores for the uppermost faces of dice still in play. Highest aggregate score after 1 round per player wins.