That's slightly ignorant to assume everyone using social media is a 12 year old girl, seeing how it's a great networking opportunity for many business people (yes adults) who aren't just there to gossip, and not much different than using a forum in some aspects (are you a 12 year old girl?) - disregarding that, I suppose I could "simplify it for you" as you put it:
People post things to their own "page" so to speak, and others can comment on it. Friends of those people can see the comments on these posts. The original post from my friend was about gay rights - I "commented" my opinion of it on my friends post, and the pastor came in with his own "comment" implying I must be homosexual and am destined for hell, gays are an abomination, blah blah, "tagging" my name in it so it became a link to my page and my friends can see it appear on their page, etc, etc. Followed up by many bible quotes that didn't apply (one did), and pushing religion down everyone's throat. No one said he had to agree with human rights for everybody, but it was offensive to him to even see rights for gays being considered and discussed apparently.
According to your definition of what people can and can't do, both me and the pasture were wrong for subjecting each other to our opinions via a mutual friends page...I think? But he actually singled me out and tagged me in the post so being the "12 year old girl" I'll say he was wrong and I'm right.
Make sense now?