Booting is a way of turning on a computer, laptop, tablet, or even a smartphone. When you press the power button, the computer starts up and starts loading all the different parts it needs in order to work. It's like getting ready for a journey, so the computer starts gathering all the things it needs, and then when it's ready, you'll see a picture on the screen - this is the boot screen. From here, it will finish loading the rest of the stuff it needs in order to work properly.