Shutter Speed
Fast shutter speed is used for things that happen in a quick instant or have a lot of movement to it, so that you can ensure you don't have a lot of blur on the photo. Fast shutter speed is best used on bright, sunny days or rooms filled with a lot of light, otherwise the pictures could come out too dark. Slow shutter speed is best used when you want to capture things over a long period of time, or the overall movement of something, like stars, or planets, or traffic flow. You should use slow shutter speed in a dark setting, because leaving the shutter eye open lets in a lot of light.