First login to your Plesk Control Panel, then -

1. Click the Domains shortcut in the navigation pane.
2. Click the required domain name in the list.
3. Click Certificates in the Services group. A list of SSL certificates that you have in your repository will be displayed.
4. Click Add New Certificate.
5. Specify the certificate properties (Make sure not to use any of the following characters in any of the fields  < > ~ ! @ # $ % ^ / \ ( ) ? , &:)
• Certificate name. This will help you identify this certificate in the repository.
• Encryption level. Choose the encryption level of your SSL certificate. Select 1024 bit from the dropdown.
• Specify your location and organization name. The values you enter should not exceed the length of 64 symbols.
• Specify the domain name for which you wish to purchase an SSL certificate. This should be a fully qualified domain name. Example: www.your-domain.com.
• Enter the domain administrator's e-mail address.
6. Make sure that all the provided information is correct and accurate, as it will be used to generate your private key.
7. Click Request. Your private key and certificate signing request will be generated and stored in the repository.
8. Download the certificate signing request (CSR) file and save it on your machine. To do this, click the respective save icon.
9. Once downloaded, open the file in a text editor, copy the all the text including the lines -----BEGIN CERTIFICATE REQUEST----- and -----END CERTIFICATE REQUEST----- to the clipboard.
10. Login to https://secure.frozenweb.co.uk and follow the instructions as detailed in your welcome email.
11. When you receive your SSL certificate, save it on your local machine or network.
12. Return to the SSL Certificates repository (Domains > domain name > Certificates).
13. Click Browse in the middle of the page and navigate to the location of the saved certificate. Select it, and then click Send File. This will upload and install the certificate against the corresponding private key.
14. Return to the domain's administration screen (Domains > domain name) and click Setup in the Hosting group.
15. Select the SSL certificate that you wish to install from the Certificate drop-down box.

If there is no Certificate drop-down box on the screen, this means that you are on a shared hosting account; therefore, you need to upgrade your hosting package and purchase a dedicated IP address from your provider.

16. Select the SSL support check box and click OK.

These instructions are based off the instructions provided in the Plesk 8 Administrators Guide