To sync user data from Clerk to a PlanetScale MySQL database using webhooks and Netlify, start by setting up a PlanetScale database and a Clerk application. Then, fork the orbytal.ink project on GitHub, deploy it to Netlify, and configure environment variables for the database connection and Clerk API keys. Next, create a Netlify Function that will act as an endpoint to receive messages from Clerk, parse the incoming event body into a ClerkWebhook object, and update or insert data into the PlanetScale database accordingly. Finally, test the function by creating an account in Clerk and verifying that the user's information is synced with the PlanetScale database, which can then be accessed directly in your application. This setup allows you to utilize Clerk for authentication and user management while still having access to users' information in your own database.