Instructions
Open up the "Happy Island" game and create a new island. Follow the tutorial and then begin playing as you normally would. You will need to reach level 5 before you will be able to throw a party -- so keep building new items and entertaining guests until you reach that level.
Continue to play the game after you reach level 5. During each level, you will be allowed to throw a party once. This happens randomly while you are playing, so continue with your island until a "Party Time" message appears on the screen. Click on "Party" to begin the process of starting the party.
Invite guests. A "Guest List" screen will appear once you accept the party. Here you will see a list of "Neighbors," who are other players in the game that you can invite to the party. Invite as many friends as you wish who are online at the time and then click on the "Send Invitations" button at the bottom of the screen to send out the invites.
Wait for the party to begin. This will happen a few seconds after you send the invitations and will be marked by fireworks, confetti and balloons floating above your island. The party will last for two hours. While it is happening, all guests to the island and neighbors will automatically get a boost to happiness.