Documentation is sparse at the moment, but not completely non-existent.
Check out my CKEDitor link survival pack from a previous question.
As a starting point, you may want to copy and use one of the existing plugins (the unpacked ones from the _source directory, of course).
The symbols
plugin is extremely simple but shows the basic points of inserting HTML into the editor
The links
plugin may be a good starting point for how to add input fields, tabs, and make them interact (If you want to go the road of understanding CKEditor's highly sophisticated dialog layout system, that is. My cup of tea, it wasn't. You may want to just set up an Iframe dialog, and do everything by yourself).