Login to your Parallels Plesk Panel
Go to the Applications tab
Locate the WordPress application and click Install
Read through the user license agreement, if you choose to accept the terms, check the box and click Next

The box titled "Specify the location where this web application should be installed" should say wordpress. Leave this as is, it should read http://yourdomain.com/wordpress

Administrative access
Select the administrative access you would like to establish for your website. The following two options are available:

• Grant administrative access to existing user: this is to be chosen when you wish the user to login to the WordPress administrative interface through your control panel. If you would like to login directly through WordPress or you would like to give another user a login see the next option.
  
• Use administrative credentials not connected to any particular user: Enter a username and password for the user. These login credentials are to login via WordPress only and no plesk panel access is granted.

The next screen will display the login information and provide a link to the Wordpress administrative interface. If you have selected to create an alternate login, this "administrative interface" link should be given to the user, along with the username and password (example: http://yourdomain.com/wordpress/wp-admin/)

Create your website; you can preview your website at http://yourdomain.com/wordpress/. Once your website is complete and you are ready to remove the /wordpress see Move WordPress, or Change the URL.
Your website is now visible at http://yourdomain.com