FOOD STAMPS SECRETS

My wife or husband & I will the two be turning 70 in 2024, so We're going to begin taking social security. I understand that 85% are going to be taxable & that we could specify approximately 22% be withheld for federal tax. So how is this completed? Is just 85% on the regular monthly check taxed at 22% or is the whole month to month volume taxed? I