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© Andrew Harrer/Bloomberg/Getty Images     December is here, and you know what that means. No, not just winter and shopping and “Star Wars” and Santa Claus. This year, December likely also means a long-awaited interest rate hike. It is widely expected that the Federal Reserve will raise rates at its policy meeting later this month, from a range of 0-to-0.25 percent to 0.25-to-0.50 percent. This, despite the small absolute change, is actually a pretty big deal. It would end the long experiment with rock bottom interest rates that started in 2008. And it would represent the first monetary policy tightening in nearly 10 years. Millions of Americans will be affected. Car loans will get more expensive. Mortgage rates will rise. Floating rates on credit cards and home equity loans will rise. Related: 10 Ways the Fed’s Looming Rate Hike Touches You But how, exactly, will Fed Chair Janet Yellen and her   cohorts actually increase the cost of credit? The simple ...