This is a ParcelJS + CraftCMS starter project. For simplicity's sake, I'm assuming you're running your site via Laravel Valet.
Copy .env.example to .env, updating variables as needed in order to connect to your local database.
Then, run yarn to install parcel-bundler.
When you're to ready to start developing, run yarn dev and navigate to your local Craft site (e.g., https://parcel-craft.test.
Note that as you save changes to either app.js or app.css, the website with instantly reload with your changes.
When you're ready for prime-time (read: PRODUCTION), go ahead and run yarn build so that the built assets get sent to the /web/dist/ directory.