How do I use shared SSL on Linux hosting?

Firstly, check in Cpanel under Security > SSL/TLS Manager

At the bottom of the page you will see the Shared SSL Certificate URLfor your website/domain.

e.g https://centos1.website-ssl.com/~username/

Use this URL to prefix any file you wish to secure in your code and hyperlinks.

e.g. https://centos1.website-ssl.com/~account/mysecurepage.php