Public_html folder is the root folder for your main site (primary domain).
Any content of the main site should be placed in the public_html directory. Parked domains (aliases) are directed in the same directory.
If in the public_html folder you have a file named index.html (or any other default file name) then it will display the downloaded site, but if you do not have a default file in the public_html folder, it will display a list of files that are in public_html folder.
The root directory of additional sites could be set up in cPanel > "Additional Domains" section.
