It depends on what kind of income you're trying to enter.
If it's SSI or VA benefits, it is NOT federally taxable.
If it's SSA (on a pink and white form),
1. Go to Your 2016 Income Summary.
2. Go down to Retirement Plans and Social Security.
3. Click Start or Update by Social Security (SSA-1099, RRB-1099).
4. Check the box by Yes, let's work on Social Security benefits.
