Re: What should a beginner know about adword?
To be honest with you, initially think of AdWords like any other business where you will have to invest before you start getting profit from it. It's actually a paid advertising platform for the advertisers wherein the advertisers compete during an ad auction process to showcase their ads on Google Network.
Here's the PDF which you should be reading as a beginner: http://static.googleusercontent.com/media/www.google.com/en/in/adwords/pdf/hc/growing_adwords_en.pdf
Here's the AdWords Youtube channel which you should view and start getting knowledge of what AdWords is all about: https://www.youtube.com/user/learnwithgoogle
Happy Reading and Best of Luck!