Hello Barheys, When you are on the report transaction detail by account report to get it to show the opening balance if you click the little cog wheel at the top right of the report next to the printer and export icon> select the blue show more and tick the box that says open balance this will then display that column on the report for you. 

The transaction detail by account shows the invoice and payment in positive and negative values to reflect the dual-entry bookkeeping system used in accounting. This approach is based on the concept of double-entry accounting, which ensures that every transaction has an equal debit and credit to maintain the balance in the books.

Credit to Debtors means it reduces the outstanding balance in Accounts Receivable/Debtors

Debit to the bank account represents the increase in cash (or cash equivalent) due to the invoice payment.