Hello there, @Mahasin,

You can only fine one box for the description of the product/service on the customize template page. However, you can enter as many descriptions as you want since the size of item description is 4095 characters. You can check out to this article for your guidance: Character limitations for fields in QuickBooks.

If you need to create another line for the item description, you can press CTRL + ENTER on your keyboard through the Invoice page. Please see the attached screenshot below for your reference.

If you wish to create a new item, please follow the steps listed below:

1. Click the Gear icon at the right top.
2. Select Products and Services under Lists.
3. Click New.
4. Select the product or service type.
5. Enter the description of the item, then click Save and close.

Feel free to read through this article for additional information with the solution provided above: How to Create and Use a Products and Services List.

If you need to create an invoice and receive customer payments, check out to this link: How to Create an Invoice.

Let me know if you have need additional information about adding an item description. I'd be glad to help.