Okay kiddo, so imagine you're playing with your toys and have a favorite one that you don't want anyone else to touch. But your friend keeps grabbing it and you want to stop them.
Now imagine your computer has different programs and sometimes you want to do something special that needs more power or special permissions. That's where su'da comes in. It stands for "Superuser Do" which means you can do something as if you were the boss of the computer.
Just like you might ask your parent or teacher for help, su'da lets you ask your computer to give you more powers temporarily. But just like you'd need to ask nicely and your parent might say no sometimes, su'da needs a special password and only certain people or programs are allowed to use it.
So when you use su'da, you're asking for permission to do something special and your computer checks if you're allowed to do it first. It's like a secret magic spell that helps you get things done!