I find that the EXIF information is great for learning the difference between settings. Almost all digital cameras record several settings in a header within the photo file. The header is called EXIF, or sometimes "metadata," and usually includes shutter speed, aperture, ISO, EV compensation, and perhaps a couple dozen more, depending on camera.
If the software that came with the camera won't show you this information, look in your photo editor for "camera information." You can also find several free- or shareware programs that will get the information for you. Use your browser search capability to find "EXIF."
It sounds highly technical, and may seem intimidating, but it's not hard to get into it and there's nothing like it for remembering what you did differently on two pictures of the same subject that obviously came out much differently.