There are two different ways to add a panel '" using requestAction or Ajax. The general rule is if the panel is pretty fast to load and content is static use requestAction. If the panel takes some time or you want to be able to interact with it then use Ajax. For example, the logs panel uses requestAction since it's pretty quick to grab the log entries and you really don't need to interact with them. The Google Analytics panel, on the other hand, takes a few seconds to query the API and has options to change the timeframe, so it uses Ajax.
New panels can either be made as a part of the application or as plugins and bundled for easy adding and removing. He shows how to write the controller and the element to interface with the CakePHP code. His example grabs the latest users created on his application.