Ask How do you add a forum to a membership site?

[SuperAffiliateX]

I want to add a forum to my membership site, but I don't know where to start. I want to ask that can I use a plugin, or do I need separate software? I want members to interact, ask questions, and share ideas easily. I also need it to be private, so only paying members can access it. Are there security settings I should enable? I'm not sure how to connect it with my existing site without causing issues. What is the best way to add a forum to a membership site?