There is a huge chance that you will be dealing with user authentication to track the users on a specific website. For example, allowing the users to log in, log out or create some resources from their personal account, which user created which resource or blocking some pages for those users who are not logged in. Users' account security heavily depends on authentication. So it's important to know how to deal with these kinds of functionalities in your web application.There are many ways to implement authentication for users, and it depends on what programming language or technology you are using. If you are using React on the front-end and Node with Express in the back-end, then you might use JWT (JSON Web Tokens) for authentication; if you are using PhP, then you will have to work with session and cookies; you can also use third parties, such as Google or Twitter, for login. So there are multiple ways to work with authentication, but it's an important concept in web development to learn and implement.