Hello sabahat.ikram,
You'll have to set up the tax code in the Tax Centre first to track VAT/GST. For QBO AE, a set of GST/VAT codes is created for you automatically.
Here's how:
Once done, you'll see the Tax Centre and a Tax/GST column on your sales and purchase forms.
If you want to add a group tax, here are the steps:
Note: You're unable to edit or delete a group tax.
You can also check answers to some common questions about VAT feature. You can read all the FAQ's here: https://community.intuit.com/articles/1775635-vat-feature-update-faq.
Please visit us soon if you have further questions.