Simple Stock Tracker (Web) App

I am designing a web application for my School project, (nothing too extensive since it has to be a simple project) its a stock tracker app. I want to create a stock tracker app using "IntelliJ IDE" along with a Vaadin Plug in. I have found some code available online and have already gotten basic framework of the app down. However I'm facing some error, which I want to resolve. What I want assistance is with editing the code and to understand it as well. Apart from that I want is to work on the existing code and add a few features to the web application.

I'm attaching a file of how the web application should look, and for which I already have the code. I want add a few more features to it, which can be further discussed.