How to make a server controlled dynamic website

I would like to make a dynamic website in which the content completely refreshes on command of the server without a page reload. I'm taking this idea off of a website that is a game called kahoot in which students enter a game pin to join a group. Once everybody is in, the teacher starts the game from their computer. Without reloading the page client side, everybody who is joined has their screen changes from the lobby screen and starts answering questions without a page reload. and at the end of the game when it is over, the page changes again. None of this is preloaded into the html when the page is first loaded. How can i do something similar. I want to know how to have pages just change when the server pushes out a command. Any insight would be great- thanks