How to you change files from PSD. to GIF. or JPEG.?

expanding on what ':]' said...she is right on how to go about it, and the reason that png looks better in most cases is that the picture is not compressed.. a jpeg has a compression ratio applied to the image by removing some of the image data, it looks pretty much the same to the naked eye, but the quality may go down slightly, this is especially apparent in low-res images. if you're doing very detailed work at low resolutions, go with png, otherwise jpg will suffice, because jpg is compressed, the file size is smaller.