To get your photos looking their best, you need to master the three basics: Aperture, Shutter Speed and ISO.
You also need to understand the relationships between these three controls. When you adjust one of them, you would usually have to consider at least one of the others, to get the desired results.
Using Auto Mode takes care of these controls, but you pay the price of not getting your photos to look the way you wanted them, and often disappointing.