The Difference

What are the differences between these three; an author, a writer and a journalist?

Sometimes I think it's so obvious and I get it, but then I realise I don't. Now I think an author is a writer who is published, a writer is someone who writes, and a journalist is one who writes news reports. 

Then what are the differences between a journalist and a reporter?

Maybe I'm making life hard. What's so important about the names! Just write whichever way you're happy with. But it's important if I'm a student, isn't it?

So what's what?