Now that we know how the interface looks, it's time to learn a bit about selection. If the adjustments required for an image concern the whole canvas, then the process is easier. We won't have to select anything. But if only a small part or object in the image requires adjustments, we will have to select it, and then apply the adjustments.
With the selection tools available in Gimp, things will be a lot easier. Here is a brief list of all the tools: