How can I start and stop only one application under a website's root node?

 
Procedure
Open IIS by typing "inetmgr" into the Run box and clicking OK, as seen in the figure below.

The IIS window will be opened.
Create a new application pool for the application that you want to stop. Right-click on Application Pool then select New -> Application Pool as shown in the following image.

Provide the appropriate name to your application pool and keep the other settings that are the defaults in the window, as shown in the following image. Click OK.

Your application pool will be created now as shown in the following image. You can observe that there is no application related to this newly created application pool. See the right-hand side. It is showing that “There are no items to shown in this view.”.

Now you need to relate this newly created application pool to the application that you want to stop. Select the application that you want to stop. Right-click then select Properties. See the following image. The following window will be opened as shown in the following image.

Click on the Create button.
 
Automatically Application Name will be enabled by IIS and it is the name of the application by default for which you are doing this activity. You can change it as you prefer. Also, the Application Pool dropdown is now enabled.
 
Now select the Application Pool that you created earlier from the Application Pool dropdown list as shown in the following image.

Click OK.
Now to stop that only application, right-click on the Application Pool name then select Stop as shown in the following image.

To start the application, right-click on the Application Pool name then select Start. In this way, you can start and stop only one application under IPlanetWebsite in which many applications are deployed under it.