Different ways to get "correct" exposures adjusting aperture and shutter speed to capture the same amount of light.

When the size of the aperture is 2x bigger (smaller f/stop), twice as much light enters into the camera. To get the same "correct" exposure, the shutter speed has to be 2x faster to let in the same amount of light.

Notice that the background and even the foreground is more blurry or out of focus as the aperture gets larger (smaller number). The "Depth of Field" (areas in focus) decreases as the aperture gets larger.