Breeding is when one male monster and one female monster breed and make an egg. When they get the egg, the monsters run away. The egg usually will hatch out to be the same monster as the male monster, unless you are doing a breeding rule. See breeding rules for more information.
Breeding rules are "rules" like a specific monster breeding with another specific monster. and a specific gender too. when they make an egg, that are not the monsters that you've used to breed. when you do a breeding rule, there will be a picture with a gray back round and a face with a question mark on it.