The passé simple, translated in English as either "simple past" or "preterite," is the literary equivalent of the passé composé, which means that it is used only in formal writing (e.g., historical and literary writing) and very formal speech. In such writing and speech, the passé simple is used alongside the imperfect, just as in everyday speech/writing, the passé composé and imperfect are used together.
You will probably never need to actually use the passé simple, but it is important to recognize it, especially if you read in French a lot (fiction or non-fiction). Fortunately, the passé simple is very easy to recognize - my high school French teacher told me that if a verb looked weird, it was probably in the passé simple, and 9 times out of 10, she was right. :-)
Go on to page 2 to learn how to conjugate the passé simple.