Here is a diagram explaining these 3 elements within the camera:
Still with me?
This brings us to the Exposure Triangle:
To take complete control of your camera by shooting in manual mode, you are going to be balancing the amount of light captured using the 3 elements we’ve been talking about: Aperture, Shutter Speed and ISO.
To do this well you need to know what effect each one has on the image you take:
APERTURE EFFECTS DEPTH OF FIELD: When you open up your aperture you are obviously letting in more light, but as a trade off you also create a more shallow depth of field. Depth of field describes how much of your shot is in focus.