The photos are taken with different shutter speeds to show the effects you can get in choosing the right shutter speed.
The first photo - You can see that the water in the waterfall is not moving, frozen into place. This shot requires a high shutter speed like 1/3000 of a second so that the camera could freeze the motion of anything moving, like cars, people, or even spinning tires!
The second photo - Unlike the first photo, the water in this one is showing us motion. This can be achieved with a low shutter speed like 1/20 or 1/10 of a second. What happens if you lower your shutter speed, lets say 3 or 10 seconds in bright sunlight. You will notice your photo will be white and too overexposed. You can try by taking shots at dawn or dusk, where the light is not too bright that time.