What is Shutter Speed?
Also called exposure time, it is how long the shutter stays open to expose light to the camera sensor. It is measured in seconds or in most cases fractions of seconds. The bigger the denominator the faster the shutter speed.
If the shutter speed is fast, it can help to freeze action If the shutter speed is slow, it can create an effect called “motion blur”, where moving objects appear blurred along the direction of the motion. This effect is used when a sense of speed and motion needs to be communicated to the viewer.
Rule of thumb!
The ‘rule’ of thumb to use with focal length is to choose a shutter speed with a denominator that is larger than the focal length of the lens. For example, a 50mm at 1/60 -unless you have super stabilization power, not the case for me-is probably ok but if you have a 200mm lens you’ll probably want to shoot at around 1/250 so not to introduce camera shake. But if using a tripod, this won't be a concern!
The final exposure doesn't only depend on the shutter speed, you can't neglect the Aperture and ISO as they bring it all together. As you change shutter speed you’ll need to change one or both of the other elements to compensate for it.