WP Fastest Cache Premium - This plugin generates static html files from your WordPress. When the page is displayed, php and mysql are used. Therefore, the system needs RAM and a processor. If many visitors come to the site, the system uses a lot of RAM and CPU, so the page is displayed so slowly. In this case, you need a caching system to avoid displaying the page again and again. The caching system creates a static html file and stores it. Other users reach a static html page.