Imagine you have a huge bookshelf (like, Hogwarts library size). You've got a new book and need to find a spot for it and later on, search it quickly every time you need it. Instead of scanning the whole shelf, you use a magical spell that tells you exactly where to place or find it. This magical spell takes the book's title and gives you a specific location, like "4th shelf, 10th spot". But remember! Even if you slightly change the book's title, the spell gives a completely different spot.

Now, let's map this to computer science: