Simple Question

So I was reading this: http://mises.org/daily/1765

And it says this:

I was just wondering what exactly is an interest rate swap and why exactly would fluctuations in the interest rate cause Freddie Mac to lose profit? I know this is simply stuff but I checked Wiki and still don’t get it.

I don’t suppose anyone is aware of any books either online of in print that would give an answer to these and other similar questions?

Wade thru this, and see if it answers your question:

http://www.lewrockwell.com/rozeff/rozeff92.html