There is a plethora of information to be had from videos on YouTube to help you understand the relationship between aperature, shutter speed and ISO. Personally, I've never really used auto except in the very early stage just to see what settings the camera chose to use as a starting point. However, auto chooses settings base on the scene, not necessarily your intended subject. I'm not going to a beat horse with information that is readily available at nauseum on YouTube, which is far better than any response you can receive here or any other forum merely because they are videos that show you step by step by step of whatever it is you want to learn, including menu settings that are camera manufacturer or model specific. You cannot beat watching someone do what it is that you want to do. Try numerous lessons by multiple presenters. The more you watch, the more you learn. Here's 4 important tidbits for you. 1) put your camera on spot metering so you meter your subject for proper exposure, not the whole scene, unless shooting landscape or other large scale subjects where evaluative metering may be a better choice. 2) Aperature controls depth of field, that is, how much is in acceptable focus from foreground to background, and in relationship to your subject. 3) Shutter speed controls motion, including compensating for camera shake - faster shutter speeds can freeze motion. 4) ISO increases/decreases the sensitivity of your sensor. Optimally, strive to shoot at your base ISO (typically 100-200) for the best quality. However, that is not always possible unless shooting outside on a sunny day. You can play with the other two (aperature / shutter speed ) to help keep the ISO down. The whole point of trying to keep your ISO down is because it introduces noise (grain) into the picture. Some handle noise better than others. You will eventually discover that ISO does not actually increase the sensitivity of your sensor, it's just the easiest way to describe the result instead of going the technical route in that it amplifies the ambient light. Soooooo... watch videos, practice and have fun! Happy shooting!