Many Photoshop and Elements tools like Opacity, Fill and the Shape tools have slider controls. You can drag the sliders to make them move or you can click the arrow next to the field and use the arrow keys on your keyboard.
Clicking the left and right arrow keys will move the slider 1% per click. You can speed up the process by holding the Shift key as you click the left and right arrow keys. This moves the slider 10% per click.
Take control of your next project by trying a new way to use the slider functions in your software.