You don't put anything on line 16 (or any other line) of the 1040. TurboTax does that based on your input in the program interview.
If you're doing a form by hand, or online fillable, line 16 is usually looked up in the tax table, based on the taxable income on line 15. But, sometimes (usually if you have qualified dividends or capital gains) a worksheet must be completed first.
Tax Tables: https://www.irs.gov/pub/irs-pdf/i1040tt.pdf