When you start using a DSLR (Digital Single Lens Reflex) camera, it is important to understand the two main factors that determine the amount of light that will fall on the digital sensor of your camera. One of them is shutter speed, the other one is aperture.
Shutter speed
Shutter speed is pretty easy to understand - it is simply the length of time that your camera's shutter will be opened for one exposure (so in fact it is more a time than a speed). Obviously, the longer your shutter will be open, the more light will fall upon your sensor.
Aperture
Aperture is basically the opening through which light falls onto the sensor. The aperture is not constant but can be set. A wider aperture will let through more light than a narrow aperture. Depending on what priority you have set, usually your camera will try to balance these two parameters to optimise the amount of light falling on your sensor. I will discuss shutter speed here and aperture in another article.
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