Google already provides us a tutorial on how we can add a domain in blogger blog. But it doesn't specifically demonstrate the steps for creating two areas - 1. Primary Domain 2. Subdomain to your two blogger blogs  i. e. you will have two websites one about main domain as well as the other about subdomain for example http: //www.bloggerwp.com and also http://demo.allbloggertricks.com. Below are usually 3 easy ways with pictures on how one can add some sort of subdomain in your blogs existing domain without any difficulty.