1. Shutter Speed
A shutter as you know in your camera allows light to hit the sensor when it is open. While taking pictures, you click on the shutter button, this opens the shutter. The hitting of light on the sensor is known as exposure and shutter speed means how long you allow the sensor to be exposed to the light.
Faster shutter speeds are meant for freezing motion . But take in mind that faster shutter speeds need a lot of light and a lot of light means alot of noise. Slower shutters speeds are used for dark situations .But slow shutter speeds can cause blur if your subject is moving.
2.Aperture
Consider an example of an open window in a dark room. When you close the window, light coming inside the dark room is less. When the window is wide open, the dark room will be lit by the light. This is the same phenomenon ina DSLR. Aperture is like an open window, expect for the values ofcourse. The bigger the values, the amount of light hitting the sensor is small and smaller aperture means a lot of light.
3.ISO Speed
ISO speed controls the sensitivity or how much light it can see. Low ISO speeds below 800 is good for outdoor photography. The higher ISO means a lot of noise. Higher ISOs are used for night time photography.