1. Log in to your Plesk Panel
2) Go to the Websites & Domains tab and select the domain you want to secure.
3) Click on ‘Secure Your Sites’.
4) Click on 'Add New Certificate'
5) Fill in the details requested and click the 'Self Signed' button
6) Return to the Websites & Domains tab and click on ‘Hosting settings’ next to the domain in question.
7) On the next page locate the Security section, select the certificate from the drop-down list and make sure that ‘SSL Support’ is checked.
8) Click ‘OK’ at the bottom of the page to save the changes.

Once completed you will have a self signed certificate to use with your website.