Where should I upload my website files?

The short answer to this question is the public_html/ directory.

Every hosting account has what is called a home directory. Within cPanel, this directory you would normally see when you connect via FTP, SFTP or SSH using your accounts primary cPanel user details.

Your website files should be uploaded into the public_html/ directory.

For example if your domain was mywebsite.com then a file located at public_html/mypicture.jpg would be served to the internet as http://mydomain.com/mypicture.jpg.

The www item is nothing more than a shortcut to the public_html/ directory - you can treat it as the same thing if you find that easier.