There are a few different ways to scale a website. One way is to use load balancing, which means that the server will send requests for pages or files to different servers depending on how many users are currently viewing them. This can improve performance and allow for more visitors to be served without slowing down the site as much as if all of them were trying to access it at once.
Another option is caching - where webpages that have been accessed before may be stored so they don't need again when next requested, saving time and bandwidth cost while not affecting accuracy or content material.
You can also cache SQL queries to improve the performance of a site significantly. Finally, a CDN can be used in order to cache content closer to the edge.