Currency Swaps

One of the big financial news stories today which apparently contributed to the bounce on Wall Street today was that the US Fed would offer an unlimited about of currency swaps with 7, 28 and 84 days terms to central banks in other countries. How do currency swaps work? In the case of a 84 day currency swap, does it go something like the US prints (or digitally creates) dollars and sends them to Euroland in exchange for a premise to pay back the US with an agreed upon number of Euros 84 days later, in effect making it a futures contract on Euros purchased with dollars that were created out of thin air? Does this practice cause the money supply to expand in the US, Europe, or both by the "unlimited" amount of currency that is "swapped"?