Fig 1 below outlines the period end dependency for Oracle Payables, Oracle Purchasing, Oracle Inventory, Oracle Receivables, Oracle Assets, Oracle Order Management, Oracle Projects and Oracle General Ledger (Release 12).

Fig 1: Period Close dependecy among the modules
If you are coming from 11i then you might see beacuse of SLA there would be additional steps you need to perform.Fig 2 will be a quick compare of steps between two versions.

Fig 2: Process and flow changes between two versions
In almost all modules the period end process consist of 5-6 major activity as:

1. Completing the Transactions
2. Creating Accounting
3. Followed by Reconcile Transactions
4. Post to GL
5. Reconcile Accounting
6. Close Period