Form 1099-SA would come from the bank or financial institution that holds your HSA account. It is not a form that you would fill out yourself. For example, if you have an HSA account at Bank ABC and you used funds from the account during the year, then Bank ABC would generate a Form 1099-SA that would detail any distributions for the account for the year. You would then enter this form into TurboTax and answer some follow up questions about it, including whether the distributions were for qualified medical expenses.
Once you have Form 1099-SA, you can enter it by following these instructions -