Function of the OBYC stand for Configure Automatic Postings. In this step, you enter the system settings for Inventory Management and Invoice Verification transactions for automatic postings to G/L accounts.
Postings are made to G/L accounts automatically in the case of Invoice Verification and Inventory Management
transactions relevant to Financial and Cost Accounting.
For example, Posting lines are created in the Stock account and Consumption account.
Read more on SAP FICO Tutorials