exposure triangle

aperture

iso

shutter speed

shutter speed is the amount of time that we keep the shutter open on the camera, like the aperture this also helps control the amount of light that hits the cameras sensor/film  the shutter speed is measured in fractions of a second for example 1/60 of a second or 1/2500 of a second

"the longer the shutter speed means the more light hits the sensor"

here is a diagram of a cameras dial used to change the shutter speed.

aperture

the aperture is simply a hole in your camera lens that opens to let the light hit the sensor/film and then closes again when the image is exposed right, the size of the hole is measured in f-stops so the smaller the number in f-stops the bigger the hole is in the lens which means more light is allowed in the camera

we can control how much light gets into the sensor by adjusting the aperture ring on the lens.

ISO

The iso is the sensitivity to the camera's sensor to light or in our case the film itself 

we can increase the cameras sensitivity on a slr camera by changing the film with an iso that suits your needs