You can't live in photography world without basic knowledge about ISO, Shutter Speed and Aperture. So what exactly they are:
ISO, Shutter Speed and Aperture definition
ISO – the sensitivity of your camera to light. A lower number representing lower sensitivity, while higher numbers mean more sensitivity. As the ISO increases, so does the grain/noise in the images. ISO may come from 100, 200, 400, 800, 1600 up to 256000 or higher
Shutter Speed – the length of time a camera shutter is open to expose light into the camera sensor. It measured in fractions of a second. Slow shutter speeds allow more light into the camera sensor and your image is brighter, while fast shutter speeds help to freeze motion. Examples of shutter speeds: 1/100 (1/100th of a second), 1/30, 1/60, 1", 2"...
Aperture – a hole within a lens, through which light travels into the camera body. The larger the hole, the more light passes to the camera sensor. Aperture also controls the depth of field, which is the portion of a scene that appears to be sharp. If the aperture is narrow, the image is sharp, while if the aperture is wide, there will be some blur area on your image. Aperture is expressed in “f” numbers. Examples are: f/2.0, f/2.8, f/4.0, f/5.6, f/8.0.
Illustration of ISO, shutter speed and aperture
How Shutter Speed, Aperture and ISO work together
ISO: mainly for control the bright of images. At the same shutter speed and aperture, when you change ISO the higher ISO, the brighter image you get, the grain/noise amount will raise too. So if you take photo in darkness, you should raise the ISO.
Shutter Speed: At the same ISO and aperture, the faster shutter speed is, the darker image you get, but you also can capture freeze motion. So if you have to take photo of something fast (car, sport, moving object...), you should set shutter speed as fast as possible. In exchange, you get darker image. If you set shutter speed to be very slow, you will get the interesting effect, and brighter image too.
Aperture: At the same ISO and aperture, the wider aperture is, the blurrer image is. If you want to create depth of field effect, or bokeh effect, set the aperture wide (1.2 to 2.8), if you want everything sharp, set the aperture narrow.
By playing with these 3 parameters, you can create a lot of exciting images.