How do I deploy this website to Vercel with a custom domain?

Create GitHub repository and push code to the repository.

Add new project to Vercel with importing from GitHub.

Let’s deploy.

Website is deployed but the domain is not custom yet. It is a random domain from Vercel.

I buy a domain from Namecheap.

Add your domain to Vercel and config Nameservers in Namecheap and wait for a while.

Now, your website is live with a custom domain.