A small frog is getting rest on water and enjoying sunshine

The frogs are some of the few remaining members of the amphibia, a group which flourished 250 million years ago. Other present-day members of the group are the toads, newts and salamanders. The amphibia are adapted, in general, to moving, feeding and breathing on land as well as in fresh water. At certain times of their life history or at particular seasons, however, they show a dependence on, or preference for one or the other.

It depends on the species of frog. The typical frogs that you will find around here all have rather large lungs and very small and delicate bones. The rest of the frog is pretty much water. These frogs can float without any further movement. On the other hand, African dwarf clawed frogs (Often sold in pet stores) take up a lot of their oxygen through their skin, and have rather small lungs. These frogs will sink to the bottom of the tank if they don't move.
But don't take ,y word for it. Right now you should have a good chance to find frogs in just about any body of water. Go and see for yourself!
Frogs, along with salamanders and newts, are members of the animal group called amphibians. Amphibians (from the Greek words amphi, meaning "both," and bios or "life") are fittingly named. Frogs start their lives as totally aquatic animals with gills and a pronounced tail fin; this is familiar to many people as the tadpole stage. Over time, legs develop, the tail and gills are absorbed, and the frog becomes a terrestrial, air-breathing animal