oh i see. So, if i went to the pet shop to buy my first male and female groupie, how do i tell what's what? how could i tell if it's a male verse a female?
http://en.wikipedia.org/wiki/Guppy
Males are going to have larger tails, a little smaller in the body and more colorful. You will want to get more females then males if you keep them in the same tank. males will endlessly harass females and if there is only one female he might stress her out enough to kill her.
It is also likely that when you buy female guppies they are already pregnant at the pet store. if your pet store keeps males and females together the females WILL be pregnant.
The pet store usually keeps "feeder guppies" in a seperate tank from "fancy guppies." These are the same fish. The only difference is the pet store tends to take better care of the fancy ones because they intend to sell them as pets and not food. Because of the quality of their in-store enviroment, feeder guppies are much more likely to have diseases that you can pass on to whatever you are feeding them to.
For this reason, if you are planning on breeding them yourself, you might as well buy a few fancy guppies. You will have more guppy fry then you know what to do with in a small amount of time. They are slightly more expensive, but have a much better chance of not infecting your tank with diseases.