If beside your bank activity you are also making or receiving payments in cash, you should import it in ThinkOut in order to keep the precision of the financial reporting.
After you have created the cash account, go to Transactions and click on Add transaction. Fill in the details and add your first cash transaction.
Add your cash withdrawals in your cash account in order to have an accurate financial reporting. If you withdraw cash from your bank account ThinkOut will identify this as an outflow, but you don't actually spend the money because it's in the cash register. Add your withdrawal as an inflow in your cash account and match the transfers between your own accounts. This way your financial picture reflects your business reality.