How to write an APA Psychology paper?

I know the format and the 4 main parts (title, summary, main, references) of the APA structure, but how exactly is the Main Body portion of the APA paper supposed to be written? I’ve never written anything more than an essay before. This has to be 5 pages not including the title, summary and references.

I also have to be base it on at least 5 “peer reviewed” journals from my Universities online journal library. What is a “peer reviewed” journal and how do I know if it is?

It is an online class at my University and my professor has been unable to contact for a while now (I think he had an emergency, and I and the rest of the class are getting worried) so I cannot ask him.

If anybody could help me out I’d be very grateful.