Magneto error: “Your web server is set up incorrectly and allows unauthorized access to sensitive files. Please contact your hosting provider”

So when I install Magento using DirectAdmin all goes well. When I go to the website I get the error “Your web server is set up incorrectly and allows unauthorized access to sensitive files. Please contact your hosting provider”.

I have checked these forums for sollutions especially this one: Magento 2: “Your web server is set up incorrectly and allows unauthorized access to sensitive files. Please contact your hosting provider”

But, I have no idea what the author of the top-comment means, and how to actually fix it. I know some basics but I forgot most of what I learned yeaaaars ago. Can anyone tell me in simple language and instructions on how to fix this?