The Cannon is a usable weapon in Sea of Thieves. They can be found on ships, or stationed on many different islands, and can be used offensively and defensively.
Cannons can fire once before needing to reload and use Cannonballs as ammunition, requiring players to carry additional Cannonballs for follow up shots.
Alternately Cannons can be used to fire players to a distant location. To use it for this purpose, the Cannon will need to be unloaded/empty. The player will have to face the end of the Cannon and interact (F) for PC (Y) for Xbox with it to load themselves. The player will be fired where the cannon is aimed. However they can directed by another player as needed.