Now, type the following command to instruct Gulp to start the Node.js server and open the browser with a local copy of SharePoint Workbench, a page you will see a lot when doing the SharePoint Framework development:

    gulp serve 

Your default browser will open and navigate to https://localhost:4321, a well-known address for SharePoint Workbench:

In this page, click the plus icon to add your HelloWorld web part to the page. The page looks like SharePoint Online, but the app menu (waffle menu in the top-left corner) is fake:

And you will see the web part in the action:

Click the pen icon to modify web part properties and change the Description property to your liking:

Next, we are going to do some investigation work on the code the Yeoman SharePoint generator created for us.