These methods have been in use since 1320 at least. We now know that the reason debits go on the left and credits on the right is that it is important that all accountants do it the same way so that any accountant can read the journal or ledger. It is the same as driving on the left side of the road. It does not matter which side of the road we drive on as long as everyone drives on the same side. The design of the ledger and journal reflect the tastes of textbook authors.
Most transactions generate one or more documents which are used in the recording process.
The source documents will lead to the recording of a journal entry. To establish and maintain an audit trail, the journal entry must contain a reference back to the source documents. The source document number is usually the best reference. Most texts use T accounts. Most bank statements are produced in running balance format.