ServerCertificate.cer = Certificate specifically for your domain / wildcard
CACertificate-1.cer = RapidSSL intermediate certificate
CACertificate-2.cer = GeoTrust CA Root certificate
For requesting the certificate, a .CSR and a private-key .KEY file have been created. - The CSR has been required for requesting the certificate and remains unused later. The private-key file is required for installation.
Important: it will only work when using ServerCertificate.cer together with the private-key that has been created together with the CSR that was used for ordering the SSL certificate. CSR/KEY/CER pairs need to be matching !
Example settings for correct certificate/key usage in Apache:
The file CACertificate-2.cer ist the root certificate. Usually all common servers already have this installed in their certificate CA store. Some server types, like nginx, do require installation of both CACertificate-1.cer *and* CACertificate-2.cer in correct order, hence the numbering in the file names.