Okay kiddo, let me break it down for you. You know how you have a special code that makes you who you are called DNA? Well, scientists made something called a "DNA-encoded chemical library" that has thousands and thousands of different codes.
But instead of codes for people, these codes are for tiny chemicals. Scientists mix all these chemicals up and keep track of them using their unique codes. Then they use the codes to find out which chemical does what.
It's like having a big box of different toys. Each toy has its own name tag on it. You can look at the name tags to see which toy is which. Scientists do the same thing with their chemical library. They can look at the codes to figure out which chemical they need for their experiment.
This library helps scientists find new medicines and treatments by testing all these different chemicals. It's like looking for a needle in a haystack, but the codes help them find it so they don't have to search through everything. Isn't that cool?