Login to Plesk Control Panel at https://plesk.colony1.net:8443/

Once logged in go to 'Domains'
Click on 'YourDomain'
Click the Files Tab downdown and choose Web Directories
Navigate to the directory in which you want to create a new virtual directory
Click, Create Virtual Directory
Name:

Path:
-(Select the Create physical directory with the same name as virtual directory check box to automatically create a physical directory with the same name as the virtual directory you are creating)
-(Clear the Create physical directory with the same name as virtual directory check box and specify the path in the field to select the physical directory that already exists)

Read permission: Check box

Directory browsing
(Select this check box to allow users to see a hypertext listing of the files and subdirectories in the virtual directory)

*It's suggested to leave anything else un-checked for a basic safe setup.

Now if you browse to the virtual directory you should be able to see all files/folders where the virtual directory points to. eg. http:// {Your_Domain} / {Virtual_Directory_Name}/