You can start your new app by running
npm run start:server and
npm run start:client. This will start up the Node.js back-end server, as well as a Webpack dev server to serve the front-end files (with things like Hot Module Replacement). Your files will be watched for changes. Any front-end changes will be seen by the Webpack server, and any back-end changes will restart the back-end server, cleaning the development database and re-seeding it as well.
npm run start:client task will show you at which local port you can access your front-end app (usually http://localhost:8080/).