Okay kiddo, so you know how a computer needs an operating system to work, right? Well, Porteus is one of those operating systems, just like Windows or MacOS.
Porteus is special though, because it is what's called a "modular" operating system. This means that you can customize it to be exactly what you want and need. It's like building your own Lego creation - you can choose what pieces you want and put them together in a way that makes sense for you.
Porteus is also really good for people who need to use a computer on the go, like if you're traveling or using a computer at a library or internet cafe. You can run Porteus from a USB drive (kind of like a really big and fast storage device) instead of having to install it on a computer. This means you can take your operating system and all your files and programs with you wherever you go, without having to worry about leaving anything behind on the computer.
So, in summary, Porteus is a special kind of operating system that you can customize to be exactly what you need, and you can use it on the go by running it from a USB drive. Cool, huh?