In order to start a discussion forum of your own, first you need to be registered and signed in to the system.
When signed in, go to your "setting" page, where you can see the "Create a new forum" section.
Choose a descriptive name to your new forum and hit the "Create" button.
Later on you may change the name of the forum to any valid name, that is not already taken.
After creating the new forum, you can apply for an account with Google AdSense. When the AdSense account is approved, you may enter the AdSense ID in the forum's admin interface. By doing so, half of the ads on your forum will be connected to your AdSense account, earning you money for the traffic in your forum. The more traffic you attract to the forum, the more money you can make.
If you already have an AdSense account, you do not need to apply for a new account with Adsense.