The $255 lump-sum death benefit is not taxable and should not be reported on your return.
In contrast, lump-sum Social Security payments (payments that include those from a prior year) may be taxable if your total income exceeds $25,000 (or $32,000 if filing jointly). TurboTax will figure this out for you.
After you enter the benefits from your SSA-1099, TurboTax will ask if you received any lump-sum payments. Answer Yes and follow the on-screen instructions. You'll need to enter the year the payment applies to along with income information for that prior tax year.
When finished, add another lump-sum payment if it's for a different prior year. For example, if you received a lump-sum payment in 2012 for tax years 2011 and 2010, you'll enter two lump-sum payments, one for 2011 and the other for 2010.
If your SSA-1099 includes fees for a Social Security or disability attorney, you may be able to deduct those. Click Federal Taxes > Deductions & Credits > Explore on My Own > then click the Start button to the right of Legal Fees, which appears near the bottom of the Your 2012 Deductions and Credits screen.