Complex sentence: Stan finds Nina, telling her he knows that she's sending high-priced U.S. stereo equipment back to the Soviet Union; he blackmails her into spying on the Russians for the FBI.
Split into simpler sentences: Stan finds Nina, where he tells her he knows that she's sending high priced U.S. stereo equipment back to the Soviet Union. With this information, he blackmails her into spying on the Russians for the FBI.