The items contained in the product backlog are defined as user stories. Basically, it tells what the user needs by telling a story which makes the feature easily understandable by everyone. It should contain enough information so developers can give a proper estimate of the working units needed to implement it. User stories should always check the INVEST (Independent, Negotiable, Valuable, Estimable, Small and Testable) criteria.
„As a logged in online customer, I want to link the credit card to my profile so that I can pay for my orders faster, without entering my credit card details at every order.“