It fires any of the 4 cannons at the Pirate Outpost (though the only one that can do anything is the one that you pass at the lower left of the outpost). You just click on any cannon there.
At the top of the mast is a "cannon starter kit" (fuses), which will fire any of the four cannons on the outpost. Push the small barrel of explosives off the mast and into the water below. Swim it over to directly under the Golden Tooth of the rock skull. Go left and fire the cannon there. Hitting the barrel will shake loose the Golden Tooth and reveal the hidden map piece.
You find the cannon starting kit and the TNT barrel. Push the TNT barrel underneath the gold tooth and fire the closest cannon to the left on the lowest cliff of the giant skull. Fire the cannon using the starter kit.
Swim left from the trading area, beneath the giant stone skull. One cannon is at the far left and you can climb up from there. To fire a cannon, you need the Cannon Starter Kit (fuse) from the very top of the outpost's mast.
on the building at the top
take the cannon kit and put it under the "cavity" then go to the cannon on the left of the cavity closest to you and fire it, it will shoot the cannon kit and shake the cavity making a piece of the map fall
You don't climb it. You have to find the cannon starting kit and explosives barrel on that island and push the TNT under the yellow tooth of the skull, fire the nearbye cannon and the map piece will be where the tooth was.
To fire the cannons at the Pirate Outpost, you need the Cannon Starter Kit (fuses), which is at the top of the main mast. Climb up from the cannon at the lower left of the skull, jumping over the pirate, and onto the roof of the Cannonry at upper right. To the left is the mainmast and the Cannon Starter Kit. On the way back down, shove the small barrel of explosives off the mast, to the left, then down into the water. Placing it under the Golden Tooth, then shooting it, will reveal the hidden map piece.
on the op of the island, there is a cannon starter kit above the pirates den. collect that, go down to another cannon and find barrel that says "DANGER, EXPLOSIVES." push it all the way under the golden tooth on the skull. Then click on the lowest cannon that will shoot the explosives which will blow up the tooth reveling the part of the map.
At the Pirate Outpost, climb up past the Cannonry to the sail, where you will find the Cannon Starter Kit (fuses). A little lower you will see a small barrel of explosives. Push it to the left, and down into the water. Place it under the giant Golden Tooth, then fire the cannon at the left side.
Go left and swim to the left side. Climb up there, then cross to the right and climb up to the Cannonry. The items you need (cannon starter kit and small barrel of powder) are on the mainmast to the left, above the Cannonry.
It is at the top of the mainmast at the Pirate Outpost, above the Cannonry and below the pirate flag. Climb up from the left, jumping over the pirate there. Go right, cross the stone skull, and jump onto the roof of the Corsair Cannons shop. On the mast to the left is the Cannon Starter Kit. On the way back down, shove the small barrel of explosives off the mast, to the left, then down into the water. Placing it under the Golden Tooth, then shooting it with the left cannon, will reveal the hidden map piece.
The small barrel of explosives is on the mast at the Pirate Outpost. Climb higher and also get the Cannon Starter Kit (fuses). Push the barrel down into the water and under the giant golden tooth. Fire the cannon at the left side to hit the barrel and blast loose the golden tooth : the map piece is under it.
First you have to push the barrel of gunpowder under the golden tooth and the get the cannons starter kit. Then go to the left bottom of the island now click on the cannon. Then you will see the piece of the map and then get it.