The main way to earn money from Google adsense is to place the ads on your website and you get money when the user clicks it.
However Google also has some other features of earning money which will be contributing very mildly in your total aggregate.
To get Adsense account has been tough nowadays. The moderation is being made very strictly and only sites with very good contents are getting new accounts. This has been the main reason that people are turning towards adsense revenue sharing sites.
To make money from Google Adsense we have to keep in mind not only the length of the content we post but also the quality of the post. Many times post with very few words also fetches more revenue than content over 1000 words and it is mainly due to relevance and the type of keyword used in the article. SO try to concentrate on keywords and also the quality of the post to get more revenue.
To get adsense account it is very difficult but not impossible. There are many sites in the net that can give you adsense account for your contribution like blogger.com, flixya.com, hubpages.com etc. So try hard and you can surely succeed one day.