Without mods, you can't.
Chat with our AI personalities
let it sit then push it in the minecart.
Left click the mine cart.
In later updates, you sit on a horse like you sit on a pig if you mean to say " how to RIDE " it then I have no idea how to do that but to sit on a horse, right click on it with a saddle and right click it
Aim your cursor in the center of the screen at the boat and right click.
To tame a bunny in the 'Bunnies' Mod, you simply right click it and it will sit on your head!