You make estimated tax payments to cover the tax on income that's not subject to withholding (self-employment income, interest, dividends, alimony, capital gains, etc.) and also when the taxes withheld from your wages are not enough to cover the tax you owe for the year. TurboTax makes sure you get credit for the estimated tax payments you made for 2016, and will help you determine if you should make estimated tax payments for next year.
To enter this in TurboTax, click on the Federal Taxes tab > Deductions & Credits > Scroll down to Estimates and Other Taxes Paid > Click on Start next to Estimates.