With reference to the link you mentioned try following steps

Ensure that you have installed mod_ssl and it is running.
Upload your certificates on Instance say /home/ec2-user/ssl
Edit /etc/httpd/conf.d/ssl.conf
Find below lines and replace accordingly (Verify the filename and path are correct)
SSLCertificateFile /home/ec2-user/ssl/certs/site.com.crt
SSLCertificateKeyFile /home/ec2-user/ssl/keys/site.key
SSLCACertificateFile /home/ec2-user/ssl/ssl_files/gd_bundle.crt
Restart Apache