Shutter Control is probably one of the most fundamental aspects of photography, it is after all, what makes a camera do its thing. When you press the button on your camera the light is received 1st into your lens, it travels through your aperture ring and then passes through the raised shutter onto either the film or digital image sensor.
Depending on how long you have your shutter set to stay open, determines how much light you are allowing in. A fast shutter time, for example 1/3000 is fast enough that the human eye has trouble seeing it, as opposed to 1/5, the human eye can easily catch this movement.
For many photographers will say that as a general rule, you should only leave your shutter open for as long as your lens is zoomed in. So, if I were shooting with my 18-105mm lens at 35mm, I wouldn’t want my shutter to be below 1/35 of a second. Unless you like blurred pictures… the exception to this rule is if you are using a tripod, or an external light source (like a flash). A tripod can provide enough stability to get a good picture, and a flash could balance the lack of light, making a suitable image.
If you are shooting long exposures (for example, waterfalls or star striping) longer shutter times are going to be needed. I would also recommend a tripod and remote to minimize unnecessary camera shake.
Another thing to consider is what your photographing, if it is action shots, you may need to use a flash to stop the motion.