Good membership sites have a forum. Again, Hostgator and Fantastico Deluxe make this easy to do. I use phpBB for my forums. The current version is 3.0.1 and you can install this into a directory on your website with one click.
To integrate your forum with Joomla!, you can use a Joomla! extension called JFusion. This will give you the ability to have members login to your site and automatically be logged into the forum at the same time. Otherwise, your users would have to login to both places.
Once your forum is installed, you should login and play around with the settings. Your first time setting up a forum will require a few days of getting to know it. phpBB is a FREE forum with powerful features. It's the same forum used here at Wealthy Affiliate.
You also have the option of selecting and installing a FREE theme for your forum. I have installed themes for phpBB and they are easy. Anyone can do it. There's no need for programming.