SSL certificate
For a long time, the only way to get an SSL (or TLS) certificate was to pay $30 or more per year. Fortunately, since December 2015, the Internet Security Research Group (ISRG) sponsored by many companies created the Let's Encrypt project and now everyone can get SSL certificates for free. Go to the Let's Encrypt website and check how to install the certificate (they have instructions for different operating systems and web servers) or if you are using Ubuntu, check the more detailed, step-by-step tutorials from DigitalOcean (for Apache or Nginx).