Exposure Triangle
The exposure triangle indicates the 3 main settings on your camera that control the amount of light let in to the sensor. The symbiotic relationship of aperture, shutter speed and ISO.
Aperture controls the size of the opening. The thing that often confuses new photographers is that the larger the opening, the smaller the number. Depending on your lens this can go as low/large as F1.2. The larger the opening the more shallow the depth of field. On the other end of the spectrum this can go as high/small as f/32. See more at the aperture page.
Shutter Speed controls the amount of time it is open for. Measured in fractions of a second this can sometimes be indicated on cameras as just the denominator (bottom) of the fraction. The longer the amount of time the lens is open the more motion blur there will be. See more at the shutter speed page.
ISO (International Standards Organisation) is not the most indicative name for light sensitivity, but that is exactly what it is. ISO is the setting for controlling the light sensitivity.
