Sales tax is an inevitable part of running a business. It's vital that you're able to easily add HST to your invoice. I'd be happy to explain how you can do this in just a few clicks.
The first step is to activate the Sales Tax module in your account. Click the Taxes tab on the left navigation menu, and if you haven't already, click Set up sales tax.
Once that's done, navigate to the invoice creation screen. Click the + New icon, then select Invoice. Once on your invoice page, enter the necessary information such as customer, product/service, and price. Then, in the Sales Tax column, select HST.