Frogs are amphibians. That means they live part of their life cycle in water and part on land. Adult females lay eggs and males fertilize them in water. There the eggs develop into embryos. When embryos hatch they become free swimming and are called tadpoles. After several days and still in the water, tadpoles develop legs and lungs and become froglets. Froglets move onto land, loose their tail and become adult frogs where the life cycle continues.
They're also super cute.