Since frogs lay their eggs in water therefore they use water for mating they undergo certain changes caused by the hormones like their color brightens, they develop sex cells etc. the male then enters the pond and attracts the female frog. Once they mate the eggs get released into the water and the male frog releases the sperms, thus fertilization occurs and the frogs leave. Now what is left is the cluster of eggs floating in the water. Because more often the female frogs do not stay with the eggs so for the protection purpose each of the egg gets encircled by a jellylike coating.
Now after a few days the life cycle process begins. The initially laid egg slowly develops into a young one and then into a proper frog. In the beginning the single cell present inside the egg multiplies itself into two, then the two cells divide into four, then these four cells become sixteen and so on... the number of cells increases in the egg, this process is called Cell Splitting. The next step is formation of the embryo by these cell clusters. Gradually embryo grows with the help of yolk and the frog features like gills start developing.
After a span of 21 days of internal development, the egg hatches and the embryo leaves the egg using a weed or underwater twigs. After coming out it develops itself into a tadpole (baby frog). These baby frogs have a long tail and they grow only till a specific limit i.e. till the time they are not big enough to swim in water on their own and feed on algae. This process can last to a maximum of 3 weeks depending on the species. In another five weeks the tadpole grows further and gets hind legs and slowly the fore legs as well on the body, even the lungs develop, the tail length also increases helping the tadpole to swim and collect food like tiny plants and putrefied animal matter.
Further as time passes the tadpole reaches to the final stage gradually. It stars to discard its horny jaws, lips and skin even. The mouth broadens a bit more, even the size of tail reduces to a minimum now and legs come up and the lungs also start functioning. Now after almost 10-11 weeks an almost developed frog is there with a very small tail almost negligible tail now. This frog, within sixteen weeks since the time of egg laying till now will grow into a proper adult frog which will continue this life cycle further