The ISO is a system used to measure the sensitivity of digital imaging systems, such as a camera's sensor or film. It basically controls the camera's sensitivity to light, allowing you to adjust the exposure in different lighting conditions.
Think of ISO like the volume on a speaker. A low volume means you need a strong signal (lots of light) to hear the sound, while a high volume means you can hear even a faint sound (low light). Similarly, a lower ISO on a camera means it is less sensitive to light and requires more light to properly expose an image, while a higher ISO means the camera is more sensitive to light and can capture an image in low light conditions.
If you're trying to photograph a subject in low light conditions, you'll need to increase the ISO to make the sensor more sensitive to light and capture the image. On the other hand, if you're shooting in bright conditions, you'll want to lower the ISO to avoid overexposure.
It's important to note that increasing the ISO also increases the amount of "noise" or grain in the image. This can be desirable in certain situations, such as adding texture to a black and white photograph, but too much noise can reduce the overall quality of the image. Finding the right balance of ISO for your specific shooting situation is an important aspect of photography.
This video discusses ISO (starts at 4mins)
This video explains ISO in detail:
This video explains ISO in a fun way:
Here is another video on ISO:
Here is another video about ISO:
Video about Film Grain Vs Noise