After clicking on Settings, you will go to settings page. Here, click on Taxes.
When you click on Taxes, you will see the next page and find all settings related to Taxes.
At this page, you can manage Tax regions and Tax calculations as your sales need.
When you click on Create discount code, you will go to next page. At this page, you will create manual code as well as generate code by clicking on Generate code. You can also add values, requirements and other settings related to discount codes.
After creating coupons and discount codes, first Save discount code from the right bottom corner of your screen and also click on Save button at the top right corner of your screen to save all the changes.