to tack onto what buck already mentioned, APA is a style of writing that basically dictates how you do in-text citations, footnotes and bibliography stuff. If this is for class, I wouldn't recommend using the internet for too much information as most teachers don't always consider the internet very reliable. By the way, APA style is standard for history papers. I'm used to MLA, which is for Enlgish papers. I taught this crap for a few years and had to abide by it for the 6 years prior...so let me know if you have any more questions.
also, if you're near a bookstore...especially a college bookstore, go in and ask for a Bedford Writing Handbook...this will have an excellent guide. The site buck posted is pretty good, but the layout in the book is much easier to follow...also, if you have a college bookstore, get it used...much cheaper.