Welcome to the forum, grandad... don't worry, you'll pick up some of the jargon as you look through these postings (and read the manual, etc.)
EXIF data is information about the camera's settings that is saved along with the picture. There are image viewers that can retrieve that info for you. So does your camera if you set the display to show it during playback; your computer may do it by just right-clicking on the filename and selecting "properties" from the menu -- depends on what operating system you are using.
Without seeing a sample image, it's pretty hard to speculate as to why some are dark on cloudy days. (EXIF info isn't as important as seeing the picture itself, so check the tips about posting photos here for us to look at.) However, I'm going to make one guess: on a cloudy day, the entire sky is often uniformly gray, and your camera may be seeing all of that grayness and interpreting it as a large light-colored background. Therefore, it's trying to make the image darker than it would if the sky were a nice clear blue. One solution is to get closer to your subject, or lock the exposure while deliberately shooting lower on the subject so the meter isn't seeing all of the sky... then re-frame and take the picture. You might also turn on the flash, so that it puts some extra light directly on your subject. (Of course, if you're shooting a distant landscape, that won't be of any help.)
Eventually, you'll be able to better see what the camera is trying to do in these situations, and can start using the Av, Tv, or manual shooting modes to get a better exposure. Meanwhile, keep on shooting, and having fun.