Every domain, to be visible to the world - has to be visible to the root name servers.
Your registrar adds your domain to their servers - then sets up a series of linkages, between the root name servers, and their own name servers. Your job, as the domain purchaser, is to connect the registrar name servers, and the Google servers.
Setting up a custom domain, for a Blogger blog, is an exciting project. You learn new concepts and skills.
Setting up a domain, from scratch, is not something to try, without experience.
If you are not an experienced DNS technician, setting up a domain, including adding it to the registrar name servers, is not a good initial project. When you are just learning about Blogger blogs and custom domain publishing, you need to concentrate on the connections between the registrar, and Google.
Let your registrar deal with the root name servers - and with setting up your domain, on their servers. Purchase your domain, including DNS hosting, from a reliable, full service registrar.
Providing your own DNS hosting can be done - but can it be done, reliably?
When you purchase only name registration, you have to act as your own DNS host. If you have a spare computer, that you can make into a name server, you can host the DNS - but is this really something that you want to do, right now?
The best full service registrars operate a worldwide network of name servers - with one hopefully located close to your readers. Can you do that, using one spare computer, in your bedroom?
You may be able to use ClouDNS (also free) for a domain host - if your registrar will work with ClouDNS.
For your first custom domain, avoid "your own DNS" and "free domains".
Neither "bring your own DNS" nor "free domain registration" are good solutions, for novice Blogger blog owners, who just want a reliable, non BlogSpot URL.
"Bring your own DNS" is a good advanced project - once you understand how custom domains work. And "free domain registration" is not a good solution, for custom domain publishing.
Budget your expenses, properly.
If you want a reliable custom domain, plan to pay for the privilege. The equipment and services, provided by a full service registrar, are not imaginary.
Don't cut corners, when setting up your first custom domain. Purchase a properly registered and setup domain, add the necessary DNS addresses, then get back to work on your blog.
An Important Update
If you did not use a Blogger / Google account when you Followed this blog, years ago, you are probably not Following now . During the past...