Writing Function Module Documentation 
Procedure
To document a BAPI, follow the steps below:
In one session, enter transaction SE37 to display the Function Builder. This is where you write the documentation.
In the second session, enter the transaction BAPI to invoke the BAPI Explorer, and to display the BAPI in the BOR for reference. In the tree view, open the relevant business object to display its BAPIs. In the Detail tab, you can view detailed information about each BAPI.
If you cannot find your BAPI in this view, display all BAPIs using the filter "Filter BAPIs according to release status", or start transaction SWO1 and enter the technical name of the business object.
The next steps are carried out in the Function Builder.
A table containing the interface parameters of the BAPI function module is displayed.
The short text should be an abbreviated description of the method in the form of <function/verb><object>. For example, "Create purchase requisition". This text is automatically used as the title of the function module documentation.
You must then copy this text in the BOR (transaction SWO1) using the appropriate function Goto -> Documentation. It is then displayed in the BAPI Explorer (Detail tab) and the BOR as the short description of the BAPI.

For an example, see
BAPI Function Module Documentation.