Get your DigiCert SSL Plesk Extension
Get your SSL certificate from inside the DigiCert extension
Install DigiCert SSL
Install the DigiCert SSL extension on your Plesk Panel, then go to extension.
Pick your certificate
Pick the certificate to suit your needs, or use the Helper on the right sidebar to help you decide
Purchase at Plesk Store
Complete your purchase at the Plesk Store.
Activate in Plesk Panel
Activate your certificate on your Plesk Panel.