Account group : The account group determines the fields for the entry screens if you
create or change a master record in the company code. The account group
also determines in which number interval the account number must be.
The account group determines:
1 . The data that is relevant for the master record
2. A number range from which numbers are selected for
the master records.
Account Group basically controls the field status of the master data.
For information on the partner funcetions you can go through the following link:
Hope this helps you....