go to google..search for adwords learning centre. U can go through the lessons provided there. Once u r thorough with them, there is a link "Sign up for Google Advertising Professional Exam [?]" on the top-right corner of the same page. U'll need to pay some 50$ to take the exam. Around 100-150 objective questions (not sure how many), duration - 1 and a half hrs. A total of 100 marks, passing is 75. Not very difficult, but be sure to be thorough with the lessons. Good luck!