What is exactly an IB Extended Essay ?

I'm just getting afraid of it. I've heard it's extremely tough. I'm mexican and I will star my Diploma course (Which will last 2.5 years) Next week, however I've heard a lot about ToK class and extended essay so I would like to star it right now, I don't know anything about the International Baccalaureat but I love learning and studying. I'm very committed with deals of school. I want to know if I can star making such monstrosity right now in order to avoid further conflicts. thanks all !