Guppies are the most beautiful live bearer and most common fish for almost every beginner. They are the cheapest fish in the store, the smallest and colourful fish and even its very easy to keep them beware that they can get diseases too. Best water temperature for them 20' - 28'C and they are very peaceful with other fish species and the perfect tank for them is planted tank. The difference between male and female is that the male is smaller and have large fins and female is much bigger with small fins (check the picture below).
The guppy can be fed with almost all food for fishes from your pet store but you shouldn't with low quality food because that will effect for their color, health and lifespan.
If you wanna breed them you should know that they get adults after 3 months so the female can produce fry and when she is pregnant she have black spot on her belly (pic)
If you want to keep the fry you shout have plants with big leaves in the aquarium so the fry can hide from the adults. They have a lot of color variables you can see that from pictures below....