If you buy your custom domain name (www URL) from GoDaddy.com follow the steps below to create a CNAME record for your custom domain.
1.Login to your GoDaddy Account.
2.Open the Domains tab and select My Domain Names. You'll be directed to the Domain Manager page.
3.Click the domain that you'd like to use with your blog.If you have one domain name click on it.
4.Click the Total DNS Control And MX Records link at the bottom of the section entitled Total DNS.
5.Click "Add New CNAME Record" in the box labelled CNAMES (aliases). If you've already created a CNAME record for your blog's address, click the pencil icon next to the existing CNAME record.
6.For the Alias Name, enter only the subdomain of the address you want to use for your blog. For example, if you picked www.mydomain.com as your address, enter "www" here.
7.For the Host Name, Enter "ghs.google.com" as the . Specify a TTL or use the default setting of 1 hour.
Click OK, and then click OK again.
8.It'll take a few hours, maybe a day or so, for this to "take". So give it a day or so,then check that "www.yourblogname.com" really does point to ghs.google.com. To do this go to Pingability.com.
In the box enter "www.yourblogname.com" (obviously changing it to your own real domain name, with the www), click Check Domain, wait a bit, and the results should say that your www points to ghs.google.com:
If your "www.yourblogname.com" really does point to ghs.google.com ,Now go to below steps.
9.Login to your blogger dashboard--> settings- ->Publishing
10.Now Click on " Custom Domain".
11.Now Click on " Switch to advanced settings".
12.Now you must enter your domain name as the picture below.
Note : you should enter the "www" part also when you give Blogger your domain name, and Save your settings.
Now you are done.Test the "www" address in your browser and hopefully it should now go to your blog and show your new domain name.
Note : To get a free co.cc domain name click here.