The exposure triangle refers to technical variables which the photographer can adjust to control the amount of light entering the camera to expose the photograph. With modern cameras this is really the easy part of photography and the use of these three variables is not dificult to master.
SHUTTERSPEED (Tv or S)
Adjusting the shutter speed controls "movement" in the picture, freezing motion (using a high shutter speed) or creating an illusion of motion (using a slow shutter speed to blur movement)
Adjusting the aperture controls the depth of focus in the picture (also known as depth of field) allowing you to maintain focus in depth with a small aperture, or to create an out of focus plain, (usually behind the main subject but not always) to isolate the main subject and reduce superflous detail in the surroundings.
ISO (also sometimes known as ASA) is a variable associated with the sensitivity of the camera's sensor to light. This setting has a bearing on the clarity of the photograph and is adjusted to faciliate photography in a wide range of light condition