The backbone of an accounting system setup is the chart of accounts. Wikipedia defines a chart of accounts like so:
A chart of accounts is a created list of the accounts used by a business entity to define each class of items for which money or the equivalent is spent or received. It is used to organize the finances of the entity and to segregate expenditures, revenue, assets and liabilities in order to give interested parties a better understanding of the financial health of the entity.
It is very likely that, if you are setting up Odoo for an existing business, you will be asked to configure the chart of accounts in Odoo to match the account structure the business is already using. Even if you are not tied to any existing chart of accounts, it is inevitable that you will need to have a firm understanding of how the accounting...