The great thing about Plesk is that the installation can be done in one complete step. To get started, log into your Plesk control panel, choose "Domains", and then click the domain where you created the CSR. Click "Certificates".
When you reach this step, you will need just one file to complete the installation. The file is included in the ZIP file that you received when your certificate was issued by VikingCloud™. You will need the .cer file - which is your actual certificate.
On the Certificates page, there should be two areas where you can upload files. Both text boxes have a "Browse" button on the right. If you click the top browse button, you can browse for your .cer file - your actual certificate.
Click Send File and the certificates will be installed on your server.
To complete the installation, click "Up Level" at the top left until you reach the domain top level. Then choose "Setup" (a house icon). Click the "SSL Certificate" drop down and change it to the certificate which you just installed.
Now, click "Server" on the left menu, and then "Server Management". Stop the Apache service, wait a moment, then start it again. Restarting will not always install the certificate properly, so a full start and stop is recommended when making certificate changes.