To use SendGrid Event Webhooks in PHP, you need to scaffold an application using Mezzio Skeleton project, install required packages, set environment variables, and create route handlers. The `SendGridWebhookHandler` class receives event webhooks from SendGrid and verifies their signature using a public key. If the signature is valid, it logs receipt of click, spam report, or unsubscribe events. A separate `SendEmailHandler` class sends test emails via SendGrid's API. The application's configuration is updated to register services for the two handlers in the DI container. Finally, the application is tested by sending an email and verifying that the event webhook receives the expected data.