DaVinci Resolve's Power Window feature is a powerful tool for color grading and correction. To use it, first, open the color grading panel by clicking on the "Color" tab at the bottom of the screen. Then, in the middle of the screen, you'll see a series of icons representing different types of Power Windows, such as a circle, square, polygon, and gradient. Click on the one you want to use.

After selecting the Power Window type, click and drag on the viewer to create the window. You can adjust the size and shape of the window by clicking and dragging the handles. Once you've created the window, any color grading adjustments you make will only affect the area within the window. You can also invert the window to affect everything outside of it. To do this, click on the "Invert" button in the Power Window panel. You can add multiple Power Windows to a single clip and adjust them independently.