Whoo boy, where to start? It might actually be more beneficial if we just come over and walk ya through it. Randomvillians, who's up for a roadtrip to Richmond?

1. Sadly Facebook is NOT in chronological order anymore. It used to be, but that was like a decade ago. You just kinda gotta roll with it.
2. When someone adds something specifically to your timeline, it's because they put it there especially for you. Your friends can all see it, too, if they visit your page. Understand that most folks do NOT visit each other's pages on a regular basis, if at all, so if other people see something a friend has posted to your timeline/page, it's usually because they are also friends with that person and it's turned up in their timeline because you're all friends.
3. When you comment on someone else's stuff, your friends can see it. If you don't want certain people to see stuff, you can change that particular person to "acquaintance" instead of "friend" and then set your default to "friends, except acquaintances" when you post stuff. Then your friends see stuff you post and comment on, but acquaintances do not. (this feature has been a big help for me to keep the family peace with some of my hillbilly relatives)
4. If you see stuff from people you don't know, it's probably someone else's friend commenting on a post that you have also interacted with (a like or comment).
5. Can't help ya with the biker thing, although that might be one of my hillbilly relatives that I somehow failed to contain.

6. Thumbs up = LIKE, heart = LOVE. There are also emojis for laughing, sad, surprised and angry/mad.
7. Messenger is kinda like a PM here on Randomville, and chatting on FB is like posting a message here on Randomville.
You'll get it eventually. And when you do, they'll change everything again. It's kinda like Facebook law or something.