Guys incompletely lost when it comes to roots what exactly do they do?

The root certificate store is a central part of distributed authentication, and of connection security, within the so-called public-key infrastructure (PKI).

The public-key algorithms are clever and elegant (and asymmetric), and provide a means to mutually authenticate participants, without exposing passwords.

In PKI, the so-called public keys are public, while the associated private keys for each public key are kept private.

The root store contains the public keys for the trusted certificate chains. While private certificate chains can be added or removed, the root certificate store is inviolable by all but Apple.

Certificates used for authentication and for encryption are mathematically tied to these so-called root certificates, and to participants’ private keys.

The root certificate store is established by, and its trust established and maintained by Apple.

The mechanisms used to authenticate and to digitally verify iOS, iPadOS and macOS updates are all also based on public key infrastructure, as are many other familiar processes and activities, including all websites using “https” connections.

For some rather more technical details and for some history: https://www.feistyduck.com/resources/