You say: "Clemmer, the theory makes sense, but how do we make it work in practice?" How do we protect information that we know should be kept confidential? In Information Technology we use the following elements: Authentication, Authorization, and Access Control.
Authentication should come first: Is the person or agent who they claim to be? In the physical world we might check a picture ID, or have them present a card and enter a PIN. Comupter systems at minimum should ask for a user ID and password.
Authorization comes next: What is this agent's role? Are they a member of a group or department that has access to the information in question? Roles can be things like Accounting, Engineering, Customer, Business Manager, and so forth.
Access Control involves what the agent can or can't do, based on their role. Can they (and should they be able to) read, write, change, add, or delete information?