What is the correct way to use a parenthetical citation in MLA style?

Hi. I'm writing a research paper on Joseph Stalin for my AP World History cl. We have to write it in MLA format but I'm having trouble using parenthetical citations. Our teacher refuses to explain MLA to us so we're on our own in that respect. I've tried everything, but I just can't make sense out of anything I've read so far that "explains" MLA. What I need is a consice explanation. Can anyone help out? Please don't post a link to any website, because I've probably read it already.