The sites configuration module allows you to setup "virtual hosts" within JAS. This way you can point multiple domains to 1 JAS instance and still serve multiple websites. Unlike most configuration modules, it allows you to add multiple site configurations, typically 1 for each domain and a default domain.
To use the functionality simply add the domain name you which to create a virtual host for and select the project that should be loaded. You can add a default virtual host by leaving the domain name empty and just selecting a project. If a default site configuration is added, a domain name that doesn't match any other site configuration will revert to the default project. If no default site configuration exists it will default to the JAS backend project.