Subject indexing is like putting labels on your toys so you can easily find them later. Imagine you have a toy box full of different kinds of toys. It might be hard to find your favorite toy if you don't know where to look for it.
Subject indexing is just like using labels to organize your toys into groups based on what they are. For example, you might have a group of toy cars, a group of stuffed animals, and a group of building blocks.
Libraries and archives use subject indexing too! They organize their books and documents into groups based on what they are about. Each group has a label, just like your toy groups do. This makes it easier for people to find the books and documents they are looking for.
Subject indexing uses specific words to describe what a book or document is about. When you search for something in a library catalog, you are asking for books and documents that are labeled with that word. Just like how you ask for your favorite toy by name when you want to play with it!
Overall, subject indexing is a way to label and organize books and documents by what they are about, making it easier for people to find what they are looking for.