Here is a PDF training material about SAP SD Billing. Billing (SD-BIL) is a component coming under SAP SD module. Billing represents the final processing stage for a business transaction in Sales and Distribution.Information on billing is available at every stage of order processing and delivery processing.
Like all parts of sales order processing in R/3, billing is integrated into the organizational structures. Thus you can assign the billing transactions a specific sales organization, a distribution channel, and a division. Since billing has an interface to Financial Accounting, the organizational structures of the accounting department, (the company codes as well as the sales organizations assigned to the company codes) are important