Adjustment layers allow you to make edits to your photo non-destructively making it easy to go back and make changes if something doesn't look quite right as you progress.
Below on the left, we have a RAW image straight out of the camera with a very warm tint overall on the right we have the same image but I've used the Color balance adjustment layer to fix the images overall tint. I'll also show you how I complete the edit making use of hue and saturation + a few other useful photoshop tools.
Let's take a look at the color balance adjustment layer and how we can use it to color grade our images in Photoshop.