About AdSense for your blog
Blogger provides a simple way for you to make money with your blog. AdSense is Google's content-targeted advertising program. If you use AdSense, you don't have to select keywords or categories for your ads. Instead, Google's servers determine what your posts are about and display the most relevant ads to your readers. For example, if you blog about baseball, you might see ads for “Major League Baseball memorabilia” next to your post. If you blog about painting, you might see ads for “Art Supplies.”
Blogger requests access to your AdSense account so that we can automatically create and place ad code on your page through our layouts and template tools. As a result of this, you might notice that Blogger is receiving "0%" of your AdSense earnings - this means that you will receive the same amount for clicks or impressions as you would creating the ad code from your AdSense account.
To view any partners that have requested access to your AdSense account, and their associated revenue shares, please log in to your AdSense account, click the Home tab, choose the Account settings sub-tab and go to “3rd-party access.” If you see an "enable access" link next to blogger.com, you must click this link in order to create ads with Blogger tools.
To take full advantage of other AdSense options and settings, such as managing the types of ads that appear on your blog, you can sign in to the AdSense site and have a look around. That's where you can see how much money your ads are earning and manage your account.
Could not retrieve earnings stats
The error message above can occur when 3rd-party Access has been disabled in your AdSense account. To re-enable access to your AdSense account by Blogger, please log in to your AdSense account, and click the Account Settings link. You'll see an enable access link next to blogger.com, you must click this link in order to create ads with Blogger tools. You will then be able to log back into blogger.com and continue setting up AdSense from the Earnings tab.
See also: What's AdSense?