Starla, This is a little experiment you can do for yourself. Val is correct in that Guppies do bear live young, but if you have a tank with other occupants I doubt you will even see the fry. I suggest if you wish to see the fry, you can buy a cheap breeder tank. This is a small plastic contraption that sits inside your main tank and there is a seperator between mother and babies. Back to the experiment.
Get a large magnifying glass, there are some specially made for fish tanks if you are so inclined. otherwise just buy a cheap plastic one. Put it against the side of your fish tank. Wait until the gravid(pregnant) guppy passes by and look at the gravid spot(dark area near her vent). If she is near to giving birth, you will be able to see the eyes of the unborn fry through her transparent skin. The fry are doubled up inside her and at any one birth she can have anything up to 40 fry.
Antoher name for the guppu is the millions fish....I wonder why