Encrypted communication usually means that the communications are encrypted using TLS encryption, as part of the communication protocol in the transport layer. Certificates are used to encrypt and sign the communication. Of course, it's crucial to be able to rely on the certificates.

Companies often operate their own certificate authorities and pre-install their root CA in their computers and software. This certainly makes sense for internal networks. It reduces overhead and potential costs compared to requesting certificates for all internal services from an official authority.

Certificates that are publicly trusted are required to be signed by one of the official certificate authorities that come pre-installed with operating systems or platforms.

Encrypted communication does not authenticate users, unless individual client certificates are being used. It lays the foundation for a secure, trusted communication.