At first you will receive a mission of destroying 8 British ships. It shouldn't be too hard, as the enemy ships are very small units which can be destroyed with one swivel guns shot.
Optional objective: Sink the fleet within the time limit - 1:30.
With the last enemy sunk, sail between the rocks to the designated spot. There you will have to fight the Protector and its guard ships.
To complete the optional objective, quickly eliminate the ship on the right by shooting it with both types of cannons and then move to the bigger ships. Only after it explodes, move to the other ships. If you can't make it within the time limits, buy the heated shot upgrade. It will make destroying the Protector much easier.