This document provides instructions for installing a certificate in Plesk 12.
CSR generation instructions can be found here.
Installing the SSL Certificate.
Once logged into Plesk, select the Websites and Domains tab and click the domain to be secured.
Click Secure Your Sites.
Select the certificate entry that was created with the CSR.
In the Upload Certificate Files section, click Browse to add the certificate and intermediate. When both files are added click Send Files.
Alternatively the certificates can be copy/pasted into the text boxes under Upload the certificate as text.
Return to the Websites & Domains tab and click Hosting Settings next to the domain.
On the next page locate the Security section and select the certificate from the drop down list. Check the box SSL support to enable the certificate.
Click OK at the bottom of the page to save changes.