Title 21 CFR Part 11 is a set of rules that big people made up to make sure that electronic documents are just as trustworthy as paper ones.
When we write something down on paper, we know it's real because we can see it and touch it. But when we write something on a computer, we can't see the actual file or document - it's all just a bunch of code (numbers and letters that tell the computer what to do).
So, the big people made rules to make sure that when things are written on a computer, they can still be trusted just like paper documents. They require things like special security measures to protect electronic documents from being tampered with, and ways to make sure that only the right people have access to them.
It's like putting something in a locked safe so no one can mess with it, but instead of a safe, it's all done with computer programs and passwords. The rules help make sure that important information is kept safe and can be trusted.