The Certificates node allows you to
Generally, Server Certificates are to be used to verify IceWarp Server users within this server. They are used by particular services when running SSL connections (HTTPS etc.). These certificates are not used for example for IceWarp WebClient.
CA (Certificate Authority) certificates verify IceWarp Server (and its users) when contacted from third parties servers. It is necessary the contacting party has this CA installed in Windows. Otherwise, the "Could not verify certificate ..." message is (usually) shown.