To generate a Certificate Signing Request using Plesk 12, perform the following steps:
Log in to the Plesk Panel.
Go to the Websites & Domains tab and select the domain to be secured.
Click Secure Your Sites.
Click Add SSL Certificate.
On the next page enter a Certificate Name to easily recognize the certificate. Fill in the required organization information for the CSR:
Click on Request.
A new entry will be added to the list of SSL Certificates. Click on the newly created certificate name to see the CSR code and Private Key.
The CSR code will be located at the bottom of the next page. Please include the tags -----BEGIN CERTIFICATE REQUEST----- and -----END CERTIFICATE REQUEST----- when submitting the CSR code for an order.
Once the certificate has been issued, follow the steps from this link to install the certificate on your server.