Hi Arbutus,
Welcome to the Community. Being able to reconcile your account is essential to ensure that your books are up to date. QuickBooks Online is a great program that offers the ability to simply track your sales and expenses. I'd be glad to help.
If this is your first reconciliation for the account, I encourage you to review the following articles.
If you've already reconciled the account, I encourage you to reach out to an accountant. They'll be able to point you in the right direction to keep your books balanced. If you don't have an accountant, you can find one near you by clicking on My Accountant on the left navigation menu> and then Find a pro to help.
If you have any other questions, feel free to reach out here.