please help, sage 50

1. What is the purpose of entering historical invoices and payments for suppliers? 2. How do you fix an incorrect payables historical invoice? 3. How do you add customers in the Receivable ledger? 4. Expense accounts created in account ledger windows are assigned by default to wha class? 5. What are the steps is setting up the 5% GST and 8% PST in SAGE