Company code hierarchy

Hello,

I'm a junior consultant for SAP FI. I'd like to know more on company code hierarchy. What is it exactly? How can it be configured in the SAP ERP?

And lastly, when creating a business blueprint ,specifically G/L accounting, how can it be represented or explained to a client?

I can't seem to find anything concise on this and few can answer me in depth.

Thank you in advance