I am new to QB and not being able to create sample invoice

Welcome to the QuickBooks Community, @amit-bedlab-co-n. I'm here to guide you in creating your very first or sample invoice in QuickBooks Online (QBO).

You're able to create and send invoices to your customers in QBO. This way, you can manage your income and sales transactions accordingly. To do this, let's go to the + New button to complete this process. Here's how:

1. Log in to your QuickBooks Online company.
2. Go to the + New button.
3. Select Invoice under the Customers column.
4. From the Customer drop-down, select a customer. 
5. Review the Invoice date. Then, from the Terms drop-down, select the due date.
6. From the Product/Service column, select a product or service. 
7. Enter a quantity, rate, and change amount if needed.
8. When you're ready to send the invoice, select Save and send. 

I've attached a screenshot below that shows the last five steps.

After that, you're able to review the status of your invoices. Just go to the Sales menu and select the All sales or Invoices tab. Then, check the Status column to see where invoices are in the sales process.

Once your customer pays, you need to record an invoice payment transaction. To do this, I'd recommend checking out this article: Record invoice payments in QuickBooks Online.

Also, you can create attractive and professional-looking invoices in QBO. With this, you're able to add the info that matters most to your business. If you wish to learn more about this, you can refer to this article: Customise invoices in QuickBooks Online.

Additionally, I want to make sure I've got everything covered. In case you've encountered an error while creating a sample invoice, you may clear your cache to remove older data that causes unusual responses to the QBO system.

Let me know how it goes in the comments below. If you have other invoice concerns or inquiries about managing your sales and income transactions in QBO, I'm just around to help. Take care always.