Mainly there are two types of blogs which bloggers offers. First is hosting on blogspot and second one is with custom domain. You can change your publishing option at anytime under your blog and your content will always remain unchanged regardless of which of these options you choose.
Set your domain within your Blogger account:
1. Once you login to your Blogger account you need to click on Settings tab and choose Basic.
2. In the “Publishing” section, click the link to add a custom domain:
3. Enter the url of the domain which you have purchased, keep in mind that it must begin with www in order to work and Click Save.
4. You should see an error, and two CNAMEs listed below. Each CNAME is composed of two parts – Name, Label or Host and Destination, Target or Points to. The first CNAME is the same for everyone, Name being “www” and Destination “ghs.google.com.” The second CNAME is particular to your blog and your Google Account, and is therefore different for each person.
5. Login into your registrar registrar panel or edit the DNS zone of your domain
6. Now it’s time to enter the CNAME’s. Where it says Name, Label or Host simply enter “www” and list ghs.google.com as the Destination, Target or Points to.
7. Now enter the second CNAME in the same way. You can also enter A-records, which links your naked domain (example.com) to an actual site (www.example.com). If you skip this step, visitors who leave off the “www” will see an error page.
8. Before you move onto the final step, wait about an hour for your DNS settings to activate. If you attempt the final step before your settings are activated, we’ll let you know with a warning message.
9. After your settings have been activated, you need to make sure Blogger knows about your custom domain so that Google can direct readers to your blog. Just head back to Blogger and update the information on your Settings | Basic tab. Find the area for “Publishing,” and click the link to add a custom domain.
10. Enter in the URL for your custom domain in the text box provided, and click Save.
11.This will do all the things. Your blogspot.com address will soon redirect to your new custom domain — be patient, as it might take up to 24 hours for the redirect to start working. If any issue persists then you suppose to recheck the DNS settings under the DNS zone of your domain.