Have you ever seen mommy or daddy use the computer at home? The computer needs something to make it work properly, like a brain so it knows what to do. This thing is called an "operating system."
Now, some people want to use their own special operating system that they like or that works better for them. They can bring it with them and use it on other computers, like when they go to school or work. This is called "bring your own operating system."
It's like bringing your favorite toy to play with at someone else's house. You can use it and enjoy it while you're there, but you don't have to leave it behind or use only the toys that belong to the other person.
Some people like to bring their own operating system when they're working on very important projects, like making a movie or designing a new video game. They might need special tools or features that their own operating system has, and they don't want to use a different one that might not have everything they need.
So, bringing your own operating system is just like bringing your own toy to play with - it makes you feel more comfortable and helps you do what you need to do.