Guppies are easy to keep. The scientific name is Poecilia reticulata.
They are live bearers. That is, the give birth to swimming fish instead of laying eggs.
Guppies can live 2-3 years in an aquarium. The males are generally much more colorful, have longer tails and a more streamlined body shape. The babies are usually born a very pale yellow-tan and develop their coloring as they grow. Guppies are "community" fish, so they like living in groups.
Guppies are known as easy to bred beginner fish and bright colors in males.
In North America guppies can be found wild in streams and ponds. The wild ones tend to be much less colorful than the "fancy" ones bred for aquariums. Never keep guppies with betta fish.