this is is an exposure triangle. Aperture simply put,aperture is a hole within a lens, through which light travels into the camera body . the larger  the aperature the more light that is let in. 

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ISO the lower the iso number the less sensative it is for it to light so basicaly it is the level of sensitivity.lower the number more sensitive the higher the number less sensative. 

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Shutter speed, also known as "exposure time", stands for the length of time a camera shutter is open to expose light into the camera sensor. if the shutter speed is fast it can help to freeze action