What is Collection?

When customer's payment is received, a collection document is required to be entered into the account.

Account Period: Select the account period of which month the customer's payment belongs to.
For example, if you received a customer payment in August, this payment is to pay the customer's arrears in June, and the account period is selected in June.
The account period is used for accounts receivable in the statement print report. 
(FINANCE - Customer Statement - Export )