COBOL developed in 1959 by a group called Conference on Data Systems Language (CODASYL). First COBOL compiler was released by December 1959.
First ANSI approved version – 1968
Modified ANSI approved version – 1974 (OS/VS COBOL)
Modified ANSI approved version – 1985 (VS COBOL 2)
COBOL/400 is the standard COBOL adopted by IBM for the AS400 system. It differentiates in the sense that the file handling for reports and sub files, indicator usage and any other feature specific to AS400 have been incorporated in it.
You get hold of the Language Reference and Programming Guide for the version of COBOL you are going to use.
Do you actually mean AS/400? Or i/Series?
Don't try search-engineing first, find out exactly which compiler you will use. Then the manuals will be readily available.