of light, therefore with two f-stops, you would only have one quarter of the light.
if you take your f-stop scale, and add your half stops, the scale is f/4, f/4.8, and f/5.6. if you then do your third stop range. it would go f/4, f/4.5, f/4.8 (for your half), f/5 and f/5.6.
don’t worry if you don’t know what all the controls on your camera mean. you can learn as little or as much as you want. after all, you can always just set it on auto and your camera will take the picture for you, and chances are it will turn out great. the manual controls are for those shots 