Imagine you enter an office store. You pick a couple of items and head to the cashier. The cashier asks you if you would like to become a Rewards Member. You accept. The cashier hands you a form asking for your contact information. Now the cashier saves you information in digital form in a Rewards Member card and gives you the card so that next time you visit the store you don’t have to fill a form again.
In this analogy the store is a website and the cookie is the Rewards Member card.