Create a new folder to store files for your website not just in /public_html? This is a change from powweb where you would “point” the domains. In SG you create new site and they handle all the work behind the scenes and each site has it’s own ftp login. There is no main directory with subdirectories for all of your sites that you control and point to.
After uploading a static site (next.js) It was driving me crazy that the site wasn’t updating right away and it was not related to my browser cache but caching on Siteground. To fix you will want to go into Siteground > Tools > Speed > Caching > Dynamic Caching and under actions click “flush cache.”