BAPI Programming guide: -
BAPI user guide: -
BAPI STEP BY STEP PROCEDURE: -
PDF download: -
There are two steps in User Exit creation.
1} Identify the User Exit suitable for the requirement and that is available in the system:
Code SE18 is used to Identify the BADI available.
Look for the string 'CL_EXITHANDLER' in the standard program. This is a class which has a method 'GET_INSTANCE' which is used to trigger BADI's from the Standard Program. The interface parameter for this static method 'EXIT_NAME' is used to pass the BADI to the method.
Open Standard Program and do a global search 'CL_EXITHANDLER'.
SE18 > give the BADI name found through above search.
CUSTOMER_ADD_DATA > which has a method SAVE_DATA.
2} Implement the User Exit identified through above process.
T.Code SE19 is used to Implement BADI.
SE19 > give the implementation name > Give the Definition name as CUSTOMER_ADD_DATA and the Short Text.
Check these blogs 2 find a BADI:
How To Define a New BAdI Within the Enhancement Framework (Some Basics About the BAdI,BAdI Commands in ABAP,
When to Use a BAdI?)
How to implement a BAdI And How to Use a Filter
Introducing Business Add-Ins
How to implement BAdi in Enhancement Framework
BAdI: Customer-Defined Functions in the Formula Builder
Difference Between BADI and User Exits
To Use BADI - Business Add In you need to Understand ABAP OO Interface Concept
Reward if useful.