Just to explain this a little more
F-Stops (or stops) are not shutter speed.
Stops is a measure for the amount of light, where the difference from one stop to another is either double the light or half the light.
This amount of light can be changed by changing EITHER the shutter speed or the aperture.
Eg Some lenses have an aperture ring where you can manually set the aperture
the f-numbers on the side might read something like this
2.8 4 5.6 8 11 16 22 32
each number here is one f-stop apart.
This means for a given shutter speed the lens will at f/2.8 (which is the f-number or aperture) let in double the amount of light (one f-stop more) than what it will at f/4.