To install AutoIndex under your domain, please follow the following steps :-
1) Login to Plesk 10.x control panel.
2) Click on "Subscriptions" and then Click on "Manage Hosting" in front of the domain.
3) Click on "Applications" icon.
4) Click on "All Avaliable Application".
5) Enter the application "AutoIndex" in the search field.
6) Click on "Install" Button on AutoIndex to install the application.
7) Accept the "License agrement" and click on "Next".
8) Select the domain under which you want to install the "AutoIndex".
9) Please enter the required details with destination directory.
Note: Please make sure to define the destination directory correctly, like /folder-name, as auto installer shall overwrite if there exists any data. If you wish to install this application to the root of the domain, just mention the directory name as / and then click on "Install".
10) Click on "Install".
11) Now you should be able to access your application via "http://yourdomain.com/folder-name" please replace yourdomain.com with your actual domain and the folder-name with the folder mentioned by you at the time of installation.