Thanks for choosing QuickBooks as one of your partners in building your business, Tomacina.

I agree with Rustler. Ideally, it's recommended to utilize a third-party app to automatically record the transactions and close open invoices in your books. Since you don't want to use another app, you'll have to manually record the invoices and payments in QuickBooks Online. Here's how:

1. Click the + New button.
2. Choose Invoice.
3. From the Customer drop-down menu, pick a customer.
4. Set the terms and invoice date.
5. From the Product/Service column, select a product or service. 
6. Enter a quantity, rate, and amount.
7. Click Save and send.

Once your customer pays you, record the invoice payments in QuickBooks Online to mark the invoices as paid. If you entered the payments in the Undeposited Funds account, you'll have to combine multiple transactions into a single record so it reflects your real-life bank activity. Then, categorize and match your online banking transactions with the payments you've already created in QuickBooks.

Lastly, I recommend visiting our Get Started page to help speed up the process of setting up one's own business in the program.

You can always visit the Community if you need additional assistance in accomplishing your other tasks.