The recommended way to start a new Vaadin project is to use Vaadin Start. It allows you to configure and download a customized starting point for your application.
Once you have downloaded a starter project and have it extracted in a local folder, you can import it to your favorite integrated development environment (IDE) and start developing it further.
If you create a project outside an IDE, you need to import it into the IDE. During development, you can run the project with a Maven target, depending on the technology stack you are using.
After you have the project in your IDE, you can go ahead and run or debug it.