Embedded in every photograph you take with a digital camera is something called EXIF data. What EXIF data physically is a record of all the settings that your camera had when you made that image, things like aperture, shutter speed, ISO, color space. Some cameras will even geo-tag your location of where the image was taken, so you can see the exact coordinates. This is cool, because unlike the days of film photography, when you'd have to pencil down everything relating to your exposure, everything is in there permanently, which makes it easy to go back and see how you shot something, where you shot something, why something might not look right.
EXIF data is kind of like a teacher, in a sense, in that you can physically see where you went wrong or where you went right, and it's broken down into simple numbers and simple values that are really easy to understand. Again, it just makes it much easier and much quicker to learn the photography basics and become a stronger photographer.
You can view your EXIF data in a number of ways. Most cameras will let you actually view it on the back of the camera, although it won't be the entirety of the EXIF data. It will be the basics of the exposures, color space and whatnot.
However, if you'd like to see more information about the data related to your photo, you can use an EXIF data viewer, programs like Adobe Photoshop, Adobe Lightroom, Photo Mechanic, Adobe Bridge. If you're on a Mac or a PC, you can generally just right-click or Control-click and view the info for the photograph, and it will be in there as well. That's EXIF data.