Domain name questions

Hello, I have a question and wonder if anybody can help me with the answer.
Thank you.

Question: You want to have internet presence, and prefer that other users
and customers should access your web site using www.xyz.com.

a) What are the first few steps to take so you can own that name?

b) Once the above steps have been taken, you now will create web site, test
it out, find a hosting company, create & set up an account, upload your
files to the remote host on the Internet. Now your web site files are
available on a host that is on the internet backbone. But when you launch
the browser and type www.xyz.com it doesn't work. Something else has to
be done. What are those?