By reading this section you are already glancing at the heart of eXo Kernel.
This section provides you the basic knowledge about modes, services and containers. You will find out where the service configuration files should be placed, and you will also see the overriding mechanism of configurations.
Finally, you will understand how the container creates the services one after the other.
Get a deeper look and read this Services wiring article. You read so much about configuration, that you should wonder what the XML Schema of the configuration file looks like.
If you wish to see examples of service configurations you should study the Core where you find descriptions of some eXo's core services. Finally you might wish to read more about PicoContainer.