When you reach the appropriate age, it’s easy to apply for Social Security retirement benefits – just go to Social Security’s website, fill out the online form and you’re essentially done. But many people overlook the next step – completing Form W-4V, which asks you how much federal income tax you want withheld from your benefits. And if you skip this step, you could face an unpleasant surprise when it’s tax-filing time, because Social Security benefits can indeed add to your taxable income.Here are the details:•If you’re a single filer… If your “com bined” income is between $25,000 and $34,000,