How do I add a tax to every expense that i have? For example, we pay 21% IVA(VAT) on everything we pay.

You can add 21% IVA (VAT) on every expense, and it requires you to use the correct region of QuickBooks Online (QBO). It looks like you're using the US version. I'd first suggest canceling it and subscribe to the QBO version specific to your country. From there, you can set up this tax rate for your expenses. I'll guide you how.

Every time you create an expense, you'll be able to select the IVA (VAT) rate in the Tax column. View the screenshot below for your visual reference.

During tax time, you can file and pay the Tax/GST you owe through the software. Just go back to the Tax Centre. Then, choose Prepare return from the Returns tab or click Record payment from the Payments tab. To learn more about this process, visit this article: File and Pay Tax/GST.

You're always welcome to drop a comment below if there's anything else you need. Have a great rest of your day, @ap37.