If you want to add an SSL on your website. you need to get an SSL certificate by paying for the certificate from a hosting company. hosting company will be providing with 3 files
once you get all these files you can go ahead and upload via cpanel or you can import them using certificate manager in AWS. you can install via command line in /etc/apache2/sites-available/default-ssl.conf file by adding the certificate file location and restart them.
I hope you understand. if you need any assistance or help in setting let me know i can set it up for you.