BDC_OKC0DE will store all the ok codes in the BDC program, 
when you pass the Fields to a scrren after filling the 
fields we need to click any button to move other screens, 
so here the Button will be have a OK_CODE internally to 
know this we do the recording of the Program, after that we 
will store this OK code in the BDC_OKCODE field to trigger 
the next operation.

Regards
Mallesh

BDC_OK code stores all ok codes.
when data from non-sap or legacy to sap format ,
the data goes to the specific field on the screen  and
when it is filled in that particular field we need to 
press enter. 
so ok_code do it automatically.

ok_code is basicaly the enter button.