如何更改网页以使登录页面独一无二？

I have a website that requires a login to go to the games section. I would like to know how to make the individual's username appear on the page they have logged into. For example, if I logged into the website with the username, 'Cooper' and the login information was correct, I would like to be able to have 'Welcome, Cooper' at the top of the webpage they have logged into. How do I do this? I have a website that requires a login to go to