While operating systems such as Windows and Linux can create their own public key infrastructure (PKI), it is much more common for organizations to use trusted companies like the common certificate authorities (CA). Web browsers know trusted authorities and allow direct connection using Secure Sockets Layer (SSL). If using an untrusted authority, such as a local operating system, the user is generally warned that the site doesnt use a trusted authority and may not be safe.
With this background in mind, identify and discuss certificate authority (CA) and PKI in your initial post.