The Brush Tool lets you apply color adjustments to a specific area instead of the whole image. To do this:

1. Adjust one or more of the color settings on the left panel.

2. Click and drag on the image to apply the color adjustments to the area you select.

If you wish to apply different color adjustments to another part of the image, then click on New Selection.

When you close this window, you will be leaving selective adjustment mode, and further color adjustments will be applied to the whole image.