As a F-1 visa holder, you are considered as "exempt" meaning not counting days for five years starting from the date of your first arrival in the United States. After the five years period, you will start counting days by using the Substantial Presence Test to see if you qualify to be treated as a US resident for tax purposes.
In your situation, you are considered as a nonresident from 2012-2016 filing a Form 1040NR. Starting from 01/01/2017, you will start counting your days. If you meet the Substantial Presence Test in 2017, you will be considered a US resident for tax purposes and file a Form 1040 for your tax year of 2017
For more examples, see :https://www.irs.gov/individuals/international-taxpayers/alien-residency-examples
