The game features two different game modes, the first being the new "Duel World" mode, where the player visits different worlds and duels unique monsters in order to reach new levels. The other, which was featured in World Championship 2007, is the World Championship mode, where the player duels duelists unlocked in Duel World. At the end of duels in both modes the player earns DP (Duel Points) that he or she can use to purchase more cards in the Card Shop. Players can also edit their deck, the look of their character, change the "Limited/Forbidden Card List", and play Tag Duels
Source: Wikipedia, "Yu-Gi-Oh! World Championship 2008", available under the CC-BY-SA License.