A posting period and year is required for any operation that requires a posting to the general ledger, including invoices, payments received and disbursed, purchase order receipts, and accounts payable vouchers.
Any window that displays a posting period and year uses the current default open posting period and year for that module. However, if you are allowed to, you can select another period and year by clicking the Lookup button, to list available periods and years.
The General Ledger module allows you to create 12 or 13 accounting periods.
Many reports and inquiries can be run by period and/or year.