Step Two: Get a "Crash and Burn" Computer
I know this is unusual advice, but we live in an age when perfectly good computers are stuffed in the backs of people's closets, or gathering dust in the garage. These are computers no one wants anymore. Grabbing one of them and using it as test vehicle has one great advantage: It removes the tension of "what if I do somethign wrong?" Who cares? It's a "Crash and Burn" computer. You got it out of the closet, and no one wanted it. Erasing the disk or losing data is no big deal.
So, find an old computer. Make sure it has does not have data anyone needs. If it's the only computer with with someone's tax returns or Christmas pictures, it is not suitable. We are going to erase it completely in the next step. Make sure it is new enough to run a recent Linux distribution. You can check that by looking at the "requirements" page for your Linux, as in this Ubuntu example.
If you don't have such a computer handy, then you can probably find one on Craigslist for less than $100, and then just erase someone else's Christmas pictures. There are very good computer surplus outlets on the web too, but shipping can be expensive.
NOTE: If you use a notebook for your "scratch" computer, you can take it on interviews and easily show off your work. The alternative, when you reach "demo stage" is to publish on a public website.