Step Three: Install a Linux Distribution
If you have a scratch computer and know how to Google, I'm sure you can handle this yourself. If you get stuck you can just Google with your other (main) computer to find the answer. Installing Linux is mostly a matter of running the installer and accepting the default choices. You should select the "use whole disk" option (or similar words) to create a purely Linux machine. Be sure to give your root user a good password, and write it down somewhere.
What is a Linux distribution? Which one should you choose? What is a root user? You can Google those things, or just use Ubuntu. It is popular now and works just fine.
If you want to stop and play at this point you can just do a bunch of installs of various Linux and BSD distributions, and using various options. I actually recommend that. You've got a scratch computer here. Install a different distribution every night for a few days, and then return to the one you like.
(This is a beautiful time to explore. You have no back-ups to worry about. Take some time and have fun.)