They describe each of these items:
- Helpers - functions/functionality to help out in the views
- Components - extra building blocks in controllers
- Plug-ins - little "applications" to add instant functionality to a site
For each, they include a more complete definition, how they fit in with the overall "Cakeness" of an application and even a bit of code to explain things. Daniel also includes a few helpful links to get aspiring coders a head start.