Account groups are maintained for a chart of account (COA) with transaction code OBD4. When you create general ledger A/c by using transaction code FS00 for a company code, you need to specifically select the group from the drop down available in the “account group” field of “types/description” tab.
By default sap will display all the account groups that are created under a COA through transaction type OBD4. These are used to organize and manage gl A/cs in a structures way for a particular company code. If you have large number of general ledger A/cs then without account groups it will be difficult to manage. For this reason, whenever a new gl A/c is created in sap, the first thing you should do is to assign an account group to it.
With this, all the gl A/cs assigned to a particular account group will have similar business functions. In transaction code OBD4 we assign number ranges to the account group which will define the numbers of gl A/cs. For example; under an expense account group with number range from 1000 to 10000, you can create an expense A/c by using transaction code FS00 with any number from 1000 to 10000. If you are trying to create gl A/c 10001 and assigning it to the expense group then SAP will not allow you to do it. Similarly sap will not allow if you are using a number less than 1000.
When you assign a gl A/c to a particular group, sap will manage appearance of the company code segment of gl A/cs i.e. all other tabs that are required to define a gl A/c will be managed by the field status setting of the account group to which the gl A/cs are assigned. With transaction OBD4 you can manage whether the company code specific settings filed for a particular gl A/c will be a required or optional or suppressed entry.
With transaction code OBD4 you define the account group name, number range of gl A/c under a chart of account. After defining, you assign those account groups to a gl A/c by using transaction code FS00.