Ask How can you use Facebook groups to grow a membership site?

[SuperAffiliateX]

I've seen many people using Facebook groups but I'm not sure how they help a membership site. I want to know if Facebook groups bring in new members or just keep the current ones engaged? Can I make the group be public or private? I also don't know what kind of content to post to keep people interested and eventually join my membership. I want to make sure it actually helps grow my site and not just take up time. How can you use Facebook groups to grow a membership site?