Hi there Assem-Zgekenova,
Thanks for reaching out about your cash accounts. QuickBooks Online is a great tool able to help you keep track of sales and expenses so you know the profitability of your company. I can point you in the right direction for assistance with cash accounts.
To set up and use a Petty cash account, you can follow the steps outlined in this article.
If you have any other questions, feel free to reach out here.