there are three main types of customer exits: function module exits, screen exits and menu exits
Function Module Exit: allows customer to add code via a function module at a specific location in an SAP application program
Format:
CALL CUSTOMER-FUNCTION '004'
Menu Exit: allows customer to add items to a pulldown menu in a standard SAP program.These items may be used to call add-on programs or custom screens.
Format:
+CUS ( additional item in GUI status )
Screen Exit: allows customer to add fields to a screen in an SAP program via a subscreen.The subscreen is called within the standard screen’s flow logic.
