What you learned: To make a selection and adjust only the selected area

A selection isolates part of an image so you can work on that area without affecting the rest of the image.

1. In the Tools panel, select the Rectangular Marquee tool. Drag a rectangular selection onto the image. The area inside the animated border represents your selection.
2. To select more, click the Add to selection icon in the options bar or press Shift and drag. To select less, click the Subtract from selection icon in the options bar or press Alt (Windows) or Option (macOS) and drag.
3. Select a layer you want to adjust. Then try applying some adjustments (Image > Adjustments). With a selection active, adjustments affect only the selected area of that layer. The same is true if you were to apply a filter, paint, fill, copy, or make other edits.
4. When you’re done, deselect by choosing Select > Deselect or pressing Control+D (Windows) or Command+D (macOS).