From among the several directories found within your Plesk account, only the following are important:
Contains all files that are part of the website. Any file and folder inside this directory is visible over the Internet unless you password protect it.
When visitors come to your site and request pages that the web server cannot find, the web server generates and displays a standard HTML page with an error message. The standard error messages may inform of problems but they do not usually say how to resolve them. You may want to create your own error pages and upload them in this directory.
DeployClick's Plesk hosting servers will check for the existence of one of the below files and based on the order specified below, display it's content as the home page, when anyone tries to list the content of any folder/directory:
If you were to upload a file index.html within the httpdocs folder of your website somedomain.com, then when someone tries to reach either somedomain.com or www.somedomain.com, then he/she would be automatically displayed the contents of the index.html file. This happens since our server treats the index.html as the home page or default page for this directory.
Similarly, if you were to upload an index.html file within the /httpdocs/plants folder, then when someone types somedomain.com/plants or www.somedomain.com/plants, then he/she would be automatically displayed the contents of the index.html file within the plants folder.
Now, if you were to upload two or more files from amongst the list given above, then the one mentioned higher in the order would be considered as the home page. So in the event that there exists an index.php and default.htm file within the same folder, then the index.php file will get considered as the home page.