It's a combination of affirmations and psychology with acupressure techniques (the "tapping" part). I've been trying it lately on some persistent issues with great success.
Check out a movie about EFT, tryitoneverything, which tells the story of ten people who get together for four days of tapping. Interspersed with their stories are interviews with authorities on energy medicine who explain why it works.
I also recommend highly Carol Look's work.