If you mate a male donkey with a mare, you get a mule. If you (more rarely), mate a male horse with a jenny, you get a hinny. That's as far as it goes, since both hybrids are sterile.
You get a mule. Thats the only way you can get a mule. Mules can't have babies.
As the others said you get a mule or a hinny. Simple but they can never bread again mule's or hinny's!