Fairies don't just have fairy forms but, they have have human forms. Their fairy or any other form is like the heart to their powers where they become stronger.
The most powerful fairy of all is Bloom, princess of Domino/Sparx and keeper of the Dragon Flame. Because of the Dragon Flame, magic and fairies exist. In each fairy stage, the fairy will become stronger than she was at first.For example, Flora earned her Believix and her Enchantix and became stronger than her Charmix.
Most fairies go to Alfea, the school for fairies. It is discovered in Season 3 that there is another fairy school named Beta Academy.