To create your taxes such as VAT, GST or any other, go to Store -> Settings -> Taxes -> Add Country.
From that popup you can now start creating your tax rules by country/states. When the rule is met for the order will assign the Tax to the total amount for payment.
If you want the prices in your store to be with the Tax included in them keep the checkbox option enabled, otherwise remove to start charging the taxes on top of the purchase amount.
