Your brain must have started to feel comfortable using UI components such as labels, text fields, comboboxes, buttons, vertical layouts, and notifications. You know how to respond to events on these components by implementing click listeners and value change listeners. You can get the introduced (or selected) values from input components, and you can wire all this up inside a custom class extending Vaadin's UI.
The rest of the trip in this book is about learning more components, how to respond to events on components, and how to make them look as we want them to look. To prepare your brain for this trip, we will right now cover some basic theory about Vaadin. So relax, close your IDE for a little while, and let your fingers have a rest while we learn some nuts and bolts of Vaadin.