Dragons did not really exist, but they are one of the world's most popular enduring mythological beasts. The myth likely originated from dinosaur bones that were found within the Earth. Ancient cultures believed these large bones to be dragons' bones.
Scientists believe that dragons as they appear in myths are an amalgamation of characteristics of several different animals, such as pythons, crocodiles and lions. The dragon's physical appearance and abilities vary across cultures and throughout time.
Since dragons were portrayed as rather large in legends it is highly improbable they'd be able to fly since that amount of mass would take incredible power to lift off the ground.