And, it helps to follow directions.
Setting up, and publishing, a custom domain is not difficult - as long as you understand the requirements.
- Get the DNS addresses right.
- Publish the blog, to the domain.
- Manage the migration process.
Get the DNS addresses right.
Once the registrar has setup the domain, your job is to use the registrar dashboard (aka the "zone editor"), and add the DNS addresses, to point to Blogger. Understand and observe zone editor syntax, required by the registrar.
Having a working DNS starts with proper registrar choice - and proper domain setup, by the registrar, on their DNS servers.
There are many things in life that can be free - but custom domain publishing won't be one. Learn about the purchase of proper service.
If you have just purchased the domain that you are setting up, check your email for a message from ICANN, and provide verified administrative email address. This appears to be a special vulnerability with Google Domains purchased domains.
99% of the people reading this will use one DNS address model. Proper DNS addresses are essential, to a stable and working custom domain.
Understand and observe DNS latency. Most registrars will use 1/2 to 1 hour latency - but some will use 3, 4, or even 24 hours.
The latency, or TTL, is set by each registrar, to help them maintain and operate their servers as best possible. If you are not otherwise experienced, use the standard registrar TTL value.
To make a stable domain more likely, wait twice the latency period, after you verify proper DNS addresses, before continuing with the second step.
Publish the blog, to the domain.
Use the Blogger dashboard Publishing wizard, at Settings - Basic, and publish the blog, to the domain. The URL published will be determined by the DNS addresses already added.
With most new domains, you will be required to verify domain ownership. This will require a second use of the zone editor - and proper use of instructions, provided by the Publishing wizard.
Once the blog is published properly, redirect the domain root to the published URL. Blogger Help would make you believe that this is an optional step - but they are wrong.
Manage the migration process.
With the domain properly published, and addresses uniformly propagated around the Internet, let your readers know about your shiny new blog address. Don't worry if some don't get the word, immediately - the BlogSpot URL will continue to work, as long as you own the blog.
Besides your readers, you should be mindful of the search engines, and of non Google services. With the blog still indexed under the BlogSpot URL, you'll get some traffic - but until the domain is indexed, you'll get less traffic than you should.
Not all non Google services will follow the BlogSpot to domain redirection - and some may have to be updated, intentionally. If you use AdSense on the blog, you will have to apply for an AdSense account upgrade - and you can apply only with the new domain operational.
The migration process is the most complicated part of the project - and it's the least predictable too. But if you remain aware of the possibilities, and plan the effort, it will go by pretty fast - and some weeks later, you'll be busy with the blog, and the domain.