To become familiar with the process of writing extensions, you might want to explore the extensions and resources that are available on the Adobe Exchange website at http://www.adobe.com/go/exchange. Installing an existing extension introduces you to some of the tools that you need to work with in your own extensions.
The Extension Manager automatically installs the extension from the Downloaded Extensions folder into Dreamweaver.
Some extensions need Dreamweaver to restart before you can use them. If you are running Dreamweaver when you install the extension, you might be prompted to quit and restart the application.
To view basic information on the extension after its installation, go to the Extension Manager (Commands > Manage Extensions) in Dreamweaver.