Skull Mountain is the first major quest in the game. The goal is to take back the amulet that was stolen from Captain Avery. This quest is split into several parts. In the first part, you must defeat 4 Troggies, scout out 3 Troggy Slingers, and sabotage the third Slinger. In the second part, you need to free a prisoner, fight 5 Cutthroats, and find the temple hideout in Skull Cave. In the third part, you free another prisoner, fight the boss Fin Dorsal, and take the amulet back to Captain Avery. He will reward you with a ship.
Note: There is currently a glitch in the free version of the game, When this glitch happens, the quest arrow points away from the temple inside of skull island and sends players into the mini-quest Clear the Vines, which cannot be completed until after the chest in the temple is opened. However, once Clear the Vines is opened, the temple is still not active, and players are stuck.