How to add GST in the sale Invoice

Hey everyone,
I am new to M-manager and my company using this software. I had seen in help there is option GST 10% when you raise a sale invoice. But I can see only below option.Please guide me how I can add Gst 10%.
Round off the total
Deduct withholding tax
Early payment discount
Late payment fees
Custom title
Thanks in advance for help.
And please let me know can I ask these kind of question here or not.

Tax codes must first be enabled for your location. The easiest method is to select your location when adding your business. The program is going through a modification right now. As a result there is no guide covering adding of tax codes if you have to change your location or add your business location after the business is already set up. This will be rectified tomorrow. Meanwhile, read the guides about tax codes.

How can this field will show up. It is not using in the my page
Please have look below for my front page

the reason it does not show is because you have not setup any tax codes.
Tax codes need to be setup under Settings.
read below guide.