PNGs are not new and are not recommended for images viewed online hehe if it is an image for the web, save as a jpg

PNGs are sometimes used when someone wants a high-color image with transparency. GIFs only support a small number of colors, JPGs support much more colors but do not support transparency. PNG combines both worlds but some browsers are still working on compatibility with PNGs (for example, Internet Explorer currently does NOT support transparency in PNGs).

GIFs are used for animations also. All those cute animated avatars and siggies you see are saved as GIFs