What is a CNAME?
A CNAME, or Canonical Name, is an entry within the Domain Name System (DNS) that specifies where someone can find your web pages. You'll use the CNAME to associate your custom domain with your blog.
After registering your domain, decide if you want to use a particular subdomain for your blog. For example, blog.mydomain.com instead of www.mydomain.com.
How Does the CNAME creation process work?
First, you'll need a corresponding CNAME record for the blog address you selected that's associated with ghs.googlehosted.com. For example, if you selected blog.mydomain.com, you will associate your blog with ghs.googlehosted.com.
Second, you need a second security CNAME record. When you try to register your domain in Blogger, the system should fail and display two security tokens. You'll need to create a second CNAME record to associate the short token (example: hqzzzn56a3ri) to the long token (example: gv-oc7x5vzzzqxirt.dv.googlehosted.com).
Note: Changes to DNS records may take up to 48 hours to take effect.