Platies are livebearers, and closely resemble their relative, the Swordtail. However, Platies are shorter, stockier and lack the extra ornamentation to their caudal fin.
Determining the sex of a Platy is relatively simple, as the males have a modified anal fin. Also, the females tend to be larger and have a bit more of a rounded body.
Breeding comes quite naturally to the Platy, so very little to no effort is needed on your part. It is a good idea to have some floating plants in the tank for the new fry. This will give them a place to hide in case the parents get the idea of eating the young. Once the fry are free swimming, move them to another tank.
Be sure to keep your aquarium well planted and well lit. If a small amount of soft green algae grows, so much the better. The Platies will actually munch on it.
This is more of an amusing site. The information isn't extremely in depth, but the entire thing is altogether fun. There's even a poem (hence the page title). If you like Platies, you should really check it out.