Following steps can be used to install SSL certificate on an AWS EC2 instance.

1. Install mod_ssl on your EC2 instance.
   • sudo yum install -y mod24_ssl
2. Get SSL certificates for your domain from https://www.sslforfree.com
   • You can also use service like https://letsencrypt.org
3. Upload the certificate files to following directories on your EC2 instance:
   • /etc/pki/tls/private/private.key
   • /etc/pki/tls/certs/certificate.crt
   • /etc/pki/tls/certs/ca_bundle.crt
4. Edit /etc/httpd/conf.d/ssl.conf file to use above paths.

   • SSLCertificateFile /etc/pki/tls/certs/certificate.crt
     
     SSLCertificateKeyFile /etc/pki/tls/private/private.key
     
     SSLCACertificateFile /etc/pki/tls/certs/ca_bundle.crt

Make sure that HTTPS traffic is allowed on your server.

For more details check https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/SSL-on-amazon-linux-ami.html

Note:

Sometimes you might also have to add chain certificate.

In such case, please visit https://whatsmychaincert.com and test whether your server is using correct chain certificate.

If not, then you can generate the chain certificate and upload to /etc/pki/tls/certs/server-chain.crt. 

Make sure to edit /etc/httpd/conf.d/ssl.conf to use appropriate path of the chain certificate.