The Application class is the entry point. The object instantiated from that class is responsible for creating and managing the user interface components. Each and every user session has its own Application object.
The fourth topic of my Vaadin Basics course focuses on this class and covers various related issues that become relevant when developing web applications using this framework. The following video clips were prepared as part of this topic.
You can find the community version of my Vaadin Basics course available for free personal usage at www.abelski.com.