Hello Ibrahim,
Please check the these books for production planning
Production Planning and Control with SAP ERP by Jawad Akhtar
Production Planning and Control with SAP Hardcover – Import, 20 Dec 2010
by Jorg Thomas Dickersbach (Author), G. Keller (Author)
The best book for me would be help.sap.com
The Forecast in SOP - Forecasting (LO-PR) - SAP Library
Best Regards,
R.Brahmankar