Where is my website? The folders in Plesk

This is how your plan is structured.

Here's how

1. httpdocs: the files of your main website. index.html or index.php in here is your home page.
2. An extra domain or subdomain has its own folder, which you choose when you create it.
3. logs: your site's log files.
4. tmp: PHP's temporary files.

Don't upload anything outside httpdocs if it needs to be publicly reachable.