Photoshopuniverse teaches you how to use the Dodge and Burn tools in a non destructive manner, in Adobe Photoshop. Dodge makes things lighter. Burn does the opposite. The problem is that this is destructive operation. Use the Brush tool at 20% opacity. Create a new layer with 50% grey. Change the layer's mode to Overlay. With the black color you will make things darker and with the white lighter. To view the changes, review the overlay layer. To correct a mistake on this layer, use a brush with 50% grey to cover up the problem areas.