As someone whose career grew up with desktop publishing, and the internet, I'm very comfortable being on a computer. I've spent a LOT of time staring at a computer screen, like I'm doing right now. Contrary to what a lot of people think, I consider being on a computer part of "Real Life". I've interacted with people In Real Life with my computer as clients, and friends, for years, and I hope to be able to continue for a long time.
If you're confused on how to act on a Facebook group page, relax, you already know how. It's the same as if you were in any group, anywhere. If you know how to behave in public, you'll be fine. If you don't, you may get in trouble. At the risk of explaining the obvious, and hurting some feelings, I'll go over some of the basics.
• Be yourself. Whether you're in a group on Facebook, or in a group like a classroom, just be you. If for some reason you feel inclined to go out in public dressed up with a secret identity, remember that it will probably make people feel uncomfortable. If you have a reason to conceal your identity, fine. If you want to be called "The Masked Avenger" and wear a mask, I'll try to understand. Your comments, however intelligent, unfortunately, will come from "the Masked Avenger", and look ridiculous.
• Don't blurt. Sorry, your mom taught you this a long time ago. Sitting in a group and suddenly blurting out the first thing that comes to mind is not the thing to do. As someone who manages a Facebook group page, I wonder about people who blurt. Yes, it's fine to be cheerful, but just saying the first thing that comes to mind, just to make noise, annoys everyone. Don't do that.
• If you like something, click the like button. If you really, really, like it, by all means write a short comment that says something like, "that's awesome!" If you've ever been in front of a group, you know how nice it is to have people express appreciation. Speaking for myself, I do a LOT of work on the Facebook page I manage, and I can't get enough of people showing their appreciation.
• Contribute. Groups are places for people to share. You can write a paragraph in the comments (I usually know some good stuff is being shared if I see a paragraph, instead of a short line with "LOL" and several exclamation points).
• Feel free to just observe. Don't feel obligated to comment. But if you do have something to share, please do so. If being on social media is new to you, it's OK to just watch. Writing "OMG" and "LOL" isn't necessary, see "blurting" above.
I hope this helps. Like I say, being on social media on your computer, or phone, or tablet, is the same as being in a group anywhere. You know how to behave, so relax. You have as much right as anyone else to be there, and you're welcome there.
Image at the top of this post: Phoenix, Arizona Historical Images, the Facebook group that I manage.