Most graphics programs create bitmap images and some create vector images too. Bitmap images lose quality when they are resized but vector images do not - they are generally less detailed and realistic than bitmaps though.
Web browsers can only display images in a limited number of file formats. To make sure your image can be displayed, save it as a JPG, GIF or PNG file.
Some graphics programs have their own file type that only they can open and save in. These are called proprietary file formats.
Photo-editing software, drawing, and painting software share many of the same features and some programs claim to do it all.