Okay kiddo, so when you want to go on the internet, you use a thing called a "web browser" like Google Chrome or Safari. Now, imagine that the internet is like a big playground with lots of different websites that you can visit and play on.
A "block" on the internet is like a fence that stops you from being able to go to certain parts of the playground. Sometimes, grown-ups or people in charge might put up a block to stop you from going to a certain website because they think it's not safe or appropriate for you to see.
It's important to remember that when someone puts up a block, they're doing it to protect you and keep you safe. Just like how your parents might stop you from crossing the street if there's lots of cars around, people who put up blocks on the internet are trying to keep you from going to places that might be dangerous or have things on them that you shouldn't see until you're older.