In Cabin Fever, players learn to become a pirate by aiding Bill Teach in running his ship, and will be rewarded with access to the island of Mos Le'Harmless. Mmors.com where sell the cheapest RuneScape Gold will give you a simple guide of it.

Go to Port Phasmatys and talk to Bill Teach. As the captain of The Adventurous, Bill needs a pirate to help him leave the port and you need to help him. Head over to the docks and board the most eastern ship. Open and search the gun locker for a Fuse and the repair locker for 4 Ropes, and pick up the Tinderbox next to the plunder chest. Go up the ship's ladder to the north and climb up the southern climbing net.

After you are on the other ship, use the Fuse with the barrel, and light it with the Tinderbox. After on board of the Adventurous, speak to Bill Teach who will ask you to repair the holes in his ship and plunder the other ship. When you have hit the ship 3 times, the ship will set sail for Mos Le'Harmless and a cut scene will occur. You will be awarded after you arrive.