Opening balance(to customers) is the sum of the amount that the customers have to pay for the business.
Opening balance(to suppliers) is the sum of the amount that the business has to pay for the suppliers.
Adding an opening balance
To add an opening balance, Go to Contacts->customers/suppliers. Either select the add button or click on edit for an existing user. There you could find a more information button, click on that and add the opening balance amount to be added for that user.