What is the difference between a post and thread?

yo idk if this is the right place to put this, so sorry if it's not. Iv been really trying to figure this place out and honestly it feels like they made things overly complicated. I understand the magazines and the federated stuff I guess, maybe. But what the hell is the difference between posts and threads. Also I have noticed that sometimes I go into a magazine that says it has posts and threads and there is nothing there. Just need a little help. I don't want to go back to reddit.