A CNC machine, like a computer, is a tool - not an end in itself. So, like buying software, you should have a job in mind and then pick the tool best suited to it. You wouldn't buy Micro$oft Office to do (just) your check book. Nor should you buy a multiaxis machining center to (just) cut ribs for your model planes.
In my case my first hobby is mobile robots. I build circuit boards for my 'bots, so my second hobby is a small (6x6) CNC machine to cut pc boards. I may go to a larger stronger machine to cut mechanical parts for my 'bots.
If you are trying to learn about CNC then your first three steps should be 1: read, 2: read, 3: read.
And then having learned what kinds of solutions are available you should read some more to find out what fits your requirements and restraints (space & budget).
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"The U. S. Navy. It's not just an adventure, it's a job."
- - the gang at Saturday Night Live