Its very simple. Borrow from the Japanese in Yen for very little interest, then convert it over to US dollars and place it in another money making instrument.
Here is a good example. Money is borrowed in Yen at little interest, then converted to dollars and then invested into treasury instruments here in the US (bills, notes, bond) at a higher rate of interest.
Zero risk. So if I borrowed 100 million dollars in yen for very little interest and then placed it in a money market account over here in the US for 5%. 5 million dollars for free and no risk. Oh dont forget we have to give the tax man some of that income. . .
There are other ways to play it, but that is very simple example.