I have tried to follow the guide, but my page does not say the same as the guide.
Several blog owners, in trying to use "Add a custom domain" to buy a domain, are observing that there is no "Check Availability" sequence.
Right now, the "Add a custom domain" link in the Publishing wizard simply goes straight to the "Advanced settings" option. This conflicts with Blogger supplied instructions.
In Blogger, locate the Publishing area under the Settings tab. Settings to Publishing.
Then, click the link to add a custom domain name, enter the domain name you'd like, and click Check Availability.
Clicking on "Add a custom domain", we are immediately presented with "Advanced settings".
Right now, we're getting very terse advice from Blogger Support.
Blogger still supports custom domain hosting, though no longer offer an option to purchase domains within the product. To purchase a custom domain, please visit a third party registrar such as GoDaddy or eNom.
Until we hear more, I'll suggest use of eNom or GoDaddy, as advised. If you choose GoDaddy, you may be able to use the Blogger / GoDaddy DNS Setup wizard, to approximate the convenience of "Buy a domain". If you can't use the GoDaddy wizard, please note that the normal rules remain in full effect.