If you have not yet created a Certificate Signing Request (CSR) and ordered your certificate, see CSR Creation | Lotus Domino SSL Certificates.
TrustedRoot.crt
DigiCertCA2.crt (if included in your zip file)
DigiCertCA.crt
your_domain_name.crt
Open Domino Server Certificate Administration (CERTSRV.NSF). This is in the System Databases in the administration panel of Notes.
Choose "Install Trusted Root Certificate into Key Ring". Enter the file name of the key ring that was made when you created your CSR, then install the Trusted Root Certificate (TrustedRoot.crt). You may get a message that the root certificate is already installed as a trusted root. If you receive this message, continue to step 3.
Again, choose "Install Trusted Root Certificate into Key Ring". Enter the file name of the key ring, then install your Intermediate Certificate(s). If your zip file includes DigiCertCA2.crt, install that file first, and then repeat this process and install DigiCertCA.crt next to this same location. Otherwise, you only need to install the DigiCertCA.crt file here.
This time choose "Install Certificate into Key Ring". Enter the file name of the Key Ring, then install your Primary Certificate (your_domain_name.crt) using the "Merge Certificate into Key Ring" button.
Your SSL Certificate is now installed in your Key Ring, and it is ready for use on your Lotus Domino Server.