Dead Man's Chest is played on land and sea, on land the player must defeat enemies, search for treasure or for comrades, items, rumors and boat enhancements can be bought from towns. When on sea the player must travel from one island to another to play through the story or to explore the world. Sea battles can take place when the Black Pearl is steered towards other boats, during these battles the cannons are fired to damage the opposing ship and once when it has been sufficiently damaged, it's possible to board the burning ship and plunder it for food, grog and even treasures.
Source: Wikipedia, "Pirates of the Caribbean: Dead Man's Chest (video game)", available under the CC-BY-SA License.