To apply free SSL certificate, go https://startssl.com/Account register an account. On "Certificates Wizard" follow the step and verify you are the domain owner, create a csr (certificate request file) on your server. After the approval that you will get a private key and the crt file. Simply Import these file to your web server, restart the service and then your HTTP connection has start protected 🙂
The certificate will be expire after one year, you can renew the certificate for free again.