Automatic account assignment determines the correct gl a/cs that need to post from the transaction types used and with other relevant factors. You need to not enter general ledger a/cs manually every time for all these types of transactions in sap.
Posting done with the customization of automatic account assignment is called automatic posting.
After doing a change to your automatic account assignment configuration when you transport it, please remember that the whole table will be transported instead of a single entry.
There are various types of automatic a/c assignment configuration done in sap. There is no menu path for such configuration. To do these types of configuration you can use transaction code FBKP.
There are some automatic a/c assignments in sap for which menu path exists. You can either use such menu path or transaction code.
Automatic Account assignment for Tax A/c
You can use transaction code OB40 or path;
Financial Accounting > Financial Accounting Global Settings > Tax on Sales/Purchase > Posting > Define Tax A/c
You will find different key to configure such a/cs. Just double click on one specific key and configure your a/cs there.
Cross company code automatic account assignment
Transaction code OBYA or following path can be used to configure cross company code settings;
Financial Accounting > General Ledger Accounting > Business Transactions > Prepare Cross Company Code transactions
Automatic account assignment for FI MM integration
You can integrate FI and MM module by using transaction code OBYC or following path;
Financial Accounting > General Ledger Accounting > Business Transactions > Integration > Material Management > Define Accounts for Material Management
Automatic Account Assignment for FI SD integration
You have to use transaction code FBKP to configure this or else following path can be used
SPRO > IMG > Sales and distribution > Basic Functions > Account Assignment > Revenue Account Determination
In all above places you assign general ledger a/c created in Financial accounting module to get it integrated with other module for direct accounting document flow in to FI.