go to setting in blogger . Settings > Basic > Publishing.
then find : Set up a 3rd party URL for your blog.
add your domain. including the www
now you see an Error with some given data
go to your host panel
Delete existing CNAME entries.
Enter the CNAMEs provided in the error message and click Save
(in DNS setting)
if your host has no DNS setting, try this free DNS panel
you can find help here too :
i should thank the NAMECHEAP.com and Dmitriy Spravtsev for very good servics and helps.