The Online Writing Lab at Purdue ( owl.english.purdue.edu/owl/resource/560/01/ ) should probably be your students' first stop for any questions regarding citation. That said, if you're a proponent of handouts, here is a pair of pretty solid APA citation guides that you could distribute to your students. The first is from the Unversity of Wisconsin (a pretty big name in academic writing), and the second is from Chabot College, a community college in California. Frankly, the guide from Chabot College is a little more visually accessible, and might be a better handout. Check them out and see which one you like!