Shutter Speed

Imagine light to be water for a moment. Your camera's shutter is like a tap that can be opened and closed to let in light. The longer it's open the more light gets in, the shorter it's open - less light gets in. This is where you get Shutter Speed from. It's the length of time your shutter is open for. If you use a fast shutter speed not as much light gets into the camera but fast speeds are great for freezing movement. A slow speed lets in more light and is great for blurring movement such as a waterfall for instance.