When in operation and used by agencies, talkgroups allow the logical grouping of radio users to ensure they can communicate with each other.
Inside a talkgroup sharing takes place to allow all radio users of a specific talkgroup to speak to one another and to the operator if applicable.
If a user in for example the SES broadcasts a message in one of their assigned talk groups, all other users on that talk group are able to hear that message. Think of it like a WhatsApp group.