Installing an SSL certificate correctly is critical for security and SEO. This guide covers: (1) Generating CSR, (2) DV, OV, EV certificate types explained, (3) Installation on Apache/Nginx/IIS, (4) Setting up Let's Encrypt with Certbot for free auto-renewing certificates, (5) Wildcard certificate configuration, (6) Certificate pinning, (7) Troubleshooting mixed content warnings, (8) Testing with SSL Labs. Includes shell commands for copy-paste.