If you already have your SSL Certificate and just need to install it, see
Lotus Domino 8.5 SSL Certificate Installation.
In the Domino Administration client, double-click on Server Certificate Administration.
Common Name: The fully-qualified domain name to which your certificate will be issued (e.g., www.domain.com or *.domain.com).
Organization: The full legal name of your company. If you are issuing the cert to an individual, the full legal name of that person.
Organizational Unit: If you belong to a sub-unit within your organization, enter that here (e.g., Marketing, IT, etc.).
City or Locality: Usually the city of your organization's main office, or a main office for your organization.
State or Province: Enter your state or province as above.
Country: If you do not know your designated country code, you can find it here.
After you receive your SSL Certificate from DigiCert, you can install it.