Hi fatemeh fardanesh,
Welcome to the Community. QuickBooks Online is a powerful program that enables you manage your accounting with peace of mind. I'll be happy to share more info and make sure you're on the right track.
To make sure we're both on the same page, could you walk me through how you created the non-zero balance on your end? If you're referring to the beginning balance, you can correct it using the steps in this article here. The article provides the necessary steps required in order to reflect the correct balances on your account.
Feel free to keep me posted on how you make out. I'll be on standby in case you need anything else.