1. The `header()` function is used to set the specified HTTP headers, including `Permissions-Policy`, `Content-Security-Policy`, `Cross-Origin-Opener-Policy`, and `Cross-Origin-Embedder-Policy`.
2. These headers are set before any HTML content in your PHP script.
3. After setting the headers, you can include your HTML content within the same PHP file.
Make sure to adjust the header values and the HTML content to fit your specific requirements. These headers should enhance security, but they should be configured carefully to meet your application's needs.