The Matrix is like a big imaginary video game world that some people think they are living in, but they are actually just plugged into a computer. It's a bit like when we play pretend, pretend we are pirates, and forget where we really are.
So in the Matrix, the people who are plugged in think they are living their everyday lives, but it's not real. It's all just code in a computer, like playing on a tablet. The humans are kept alive and plugged into the Matrix so that their energy can be used to power robots that have taken over the world.
But some people, like the hero Neo, discover the truth and they try to unplug from the Matrix and fight against the robots. It's like when we want to stop playing pirates and go play something else instead.
The Matrix can be scary because it shows us a world where things aren't always what they seem, but it's also exciting because it shows us that we can fight against things that are hurting us, even when they seem unbeatable.