How do I follow stuff on Facebook?

I am trying to find out how Facebook works. It is unclear to me. 500 million people seem to understand it, but I don’t.

The most presssing question is: What appears in my News Feed? Posts from friends appear, but when I like pages or join groups, I can’t find a way to get news from those walls to my own homepage / newsfeed.

That could be consistent, but when I liked ” Costa Rica” which is apparently a “local business”, posts DO appear in my News feed.. Why? Who can explain?