A pony is tameable by giving the pony girl a cell phone and paying her 50 dollars. Once you have done those things, the Ponycloud will deliver your pony. They start off really small, the size of an ant, and grow when fed wheat, sweets (e.g. cake, cookies, lollipop, etc) and water. A pony is very needy and if you do not watch it, your pony may get sick and die (Unless you give it medicine). You may also give your pony armor (diamond boots are recommended), ride your pony off into the sunset, enjoy the day adventuring, or have it help you fight your dangerous mobs in Minecraft.
Tip-Keep them away from Hotdogs. Ponies and Hotdogs don't get along well. The pony will eventually end up killing your hotdog.