If you've ever tried shooting a video while walking or running, you know what it looks like. Shaky, blurry, and nauseating in some cases.
You are holding the camera with your hand, which is directly connected to your moving body. That means all the shock that is created with each step is transferred up your body, through your arm, into the camera, causing it to shake. The intensity is different whether you're on rocky terrain or flat ground, but it is very hard to prevent this, even if you try to "slide walk"
One possible solution to this is extremely simple. Attach the camera to a tripod, then hold the tripod as you film the video. The tripod acts as a counterweight that absorbs shock. Little vibrations are essentially "ignored" by the tripod, making the video less shaky. Because the tripod is heavier and you are not holding the camera directly, the camera is less likely to suddenly move. Instead, it will sway gently, which is at least better than wild vibrations.
You can only point the camera in one direction, and can't adjust its pitch (up and down). If you try to do so, the vibrations may return.
The biggest advantage is that it reduces shaking, but you can also use the tripod to lift up your camera to 9 1/2 feet or so above the ground, which allows you to take pictures and have a higher range of shots.