Before your start your journey with a system like SAP, you need to have your business structure very well defined.
SAP gives the option to configure a Company, and inside this Company, you can create Company Codes that are the ones that control the accounting for each enterprise.
You can have as much Company Codes associated to a Company as needed, and this is because each Company Code represent an accounting book.
Below this, and by below I only mean in configuration steps, are the business areas, that are very important entities inside SAP, because they represent work areas that are independent of a Company Code and you can post to them also.
With only this two examples you are able to create reports and information, for a Company Code, for a Work Area, or combined.
To understand more about this configuration, and how to implement it on SAP refer to this course that explains how to implement SAP Financials configuration for only $20 USD: