In Chapter 1, Looking Back, Looking Forward, I gave you a rundown of all the new controls available in the new UI framework, namely:
The Text control
The Image and RawImage controls
A Button control
A Toggle control
The Scrollbar and Slider controls
It may not sound like much (compared to the larger array of controls in the legacy GUI), but as you'll discover, it's all you really need as a base (especially when you combine them with all the other features of the new UI).
Beyond that, Unity also provides you with a fully extensible framework used to craft your own controls with events, structures, and design patterns to enable just about whatever you can dream up. You can even use another component called the Selectable component, that can be added to just about any other GameObject (on a Canvas) to enable user interaction.
Enough preamble, let's play.