Well do you plan to do other things with your server box like adding a plex server?
If not then I can’t suggest using FreeNAS as your first linux os. I would try out either Ubuntu or Lubuntu desktop versions to learn how to use linux.
What kind of machine are you using? Is it a prebuild system, laptop or did you build your own system?
Also if possible, do watch this video for an introduction to linux. It is an hour long and it goes in-depth of what linux is and how to use it. https://youtu.be/YdtfuAJUce4?t=182
I am using it for a plex server, and was able to accomplish what I needed to do with mine-os.
Those to guides were very helpful. I went from there and found some more guides and resources to be able to run in the shells of Nas and the JAIL and was able to get a server imported.
This definitely has a learning curve but its been fun.