Hi Ahmed,
Please refer SAP help like it will guide you how to create reference characteristics in sap.
https://help.sap.com/saphelp_erp60_sp/helpdata/en/ec/62aad1416a11d1896d0000e8322d00/frameset.htm
Reference Characteristics and the Configuration Engine - Configuration Engine - SAP Library
Regards,
R.Brahmankar