Okay kiddo, so you know when you use the internet to play games or watch videos? Well, grown-ups who work with computers sometimes do experiments on the internet to learn new things. Just like how you might do an experiment in science class to learn about something new.
An internet experiment note is like a report that the grown-ups write to explain what they did in their experiment and what they learned from it. They write down everything they did step-by-step, like a recipe, so that other grown-ups can try the same experiment and see if they get the same results.
Sometimes these experiments are about how people use the internet or how different websites work. Other times they're about something called "internet security," which is like making sure bad people can't do bad things on the internet. Whatever the experiment is about, the grown-ups share their notes with each other to learn new things and make the internet better for everyone to use.