After submitting your application, it will take around 24 hours to know whether you are approved to place advertisements on your site or you have to improve your site before you can be the part of AdSense Publishers. In case your application is approved, then you can log into AdSense account to get the Ad Code which you will be placing on your website guy.
Once you are logged in to you AdSense, click on "My Ads" tab and then press "New Ad Unit" button.
This will take you to “Create Ad unit wizard” where you can customize your ad size, color, ad type and etc.
Selecting AD Size: AdSense offers wide range of Ad sizes so that you can select the one which fits your needs as well as your website’s design. The recommended ad sizes includes 400x350,828x90 or etc. why, because these ads are more likely to provide you high earning opportunities. In other words, you can say that these ads are of higher potential to provide you more earning on each ad click.
Once you are done with customizing your ad unit, simply press “Save and get code”. A new window will pop-out providing you the code of the ad you just created. Now copy the ad code as we will need it in the next step.
That’s all, you have successfully added Google AdSense on your blogger site.