GST is an indirect tax applied to the supply of goods and services. (Reference link:What is a Tax?)
To create a Tax, go to Ordering→Taxes→click on Add Tax
Title: Enter the title/name of the tax you are creating. Preferably this would be SGST, CGST, or GST.
CRM Title (Optional field): You can enter a title purely for your reference. Details entered in this field will not reflect on the UI of any platform.
Description (Optional field): You can describe the tax that you are creating. The description will not reflect on the UI of any platform.
Active: Enabling or disabling this flag would determine if the tax will be applicable to the items or not.
If the active flag is unchecked, the tax will not get applied to the items on the aggregators. This would lead to inconsistencies in billing.
Type: You can either select Applicable to Fields or Fixed Value. Since the tax is a dynamic amount that is calculated on the price of items added to the cart, you will have to choose Applicable to Fields from the drop-down.
Once you select Applicable to Fields from the Type drop-down, 3 more fields appear below: Fields, Type, and Value.
Field: A bunch of options will be available from the drop-down, but since tax is only applicable on an item price, choose Item Price from the list.
Type: Since the tax is calculated only on a percentage basis, select Percentage from the drop-down list.
Value: Add the percentage value that will be calculated on the item price.
(SGST and CGST - 2.5 or GST - 5)
The sum total of tax calculated on every item added on the cart will be added to the order subtotal.
Once done, click Save.
After saving, new fields on the page will appear: Item Group and Location Group.
By default, you will see All added as a pair in both Item Group and Location Group fields which would imply that this tax is applicable on all items and all locations configured on the portal.
In case you have only a particular set of items or locations on which this tax needs to be applied, you can go ahead and create an Item Group or Location Group or both (Reference links: Item Groups and Location Groups).
Provided the respective groups are already created, delete the default pair (which is All items and All locations), click Add New Pair, and select the desired Item Group and Location Group where this tax has to be applied from the options available.