f-stop and Aperture Size
In order to understand what your f-stop value means, it is helpful to think in terms of fractions. The f-stop number is the bottom number of a fraction that represents the amount of light getting into the camera. Therefore f2 is 1/2 and f16 is 1/16. Since 1/2 is much larger than 1/16, the aperture is more open at f2 than at f16.