Intro To Manual Mode
In this mode, your camera essentially grants you complete control over the various exposure settings also called the exposure triangle, which include Shutter Speed, Aperture, and ISO, allowing you to capture images exactly as you envision them.
3.ISO
Think of it as a volume knob on your headphones. ISO does not actually increase the amount of light that is hitting your sensor; it is only amplifying the signal that is already present. For example, during a basketball game, after you have made the necessary adjustments to your shutter speed and aperture to minimize any blur in the images, if you notice that the final image is still very dark, you should consider increasing your ISO in order to properly expose the image. Just remember, however, that the higher the ISO number you choose, the more grain or noise you will introduce to the image, which can affect the overall quality, althoug bigger sensor sizes may let you get away with higher iso.
The faster you master and understand these settings will make it easier for you to gradually focus more on finding your style and approach to photography.