I am not a tax professional, but I am experienced with many aspects of taxes.
It sounds like you are using Form 1040A.
Line
14a should contain the total Social security benefits for you and your spouse (if spouse is applicable). This amount should match the sum of the amounts on Form SSA-1099, box 5, for you and your spouse.
Line 14b is the taxable portion of the amount on line 14a. The amount on line 14b is usually less than or equal to the amount on line 14a. This because for many people, not all of their social security benefits are taxable. TurboTax calculates the taxable amount and places it in line 14b.
If you want more information, you can look at the IRS instructions for Form 1040A for these lines (on pages 29 - 31). See https://www.irs.gov/pub/irs-pdf/i1040a.pdf
