Always have back ups! Do you have time machine set up? I personally keep all important files on a harddrive. So if I need to reboot my computer I'm not worried.
But so far I have not needed to do that. If it's REALLY that bad, you can take your computer to an Apple store and they can redownload the whole OS. 
If you are following tutorials and doing your own research I don't think you'll have severe problems. Just don't delete things you're not sure about. 
The reason I suggested a VM is because its fairly easy to set up, and you can get familiar with the interface. Hopefully giving you the confidence and motivation. And when you are ready you can buy a whole machine just dedicated to Linux. 

 Oh time machine needs a set-up? I haven't done it. I also will look it up. 

Thank you. Didn't know about VM options. So you helped me. 

I am looking into de-apple myself. But, it is cheaper to use my current computer to practice Linux for now.  
 

 Yes time machine needs to be set up. You can control how often it backs up your data. I recommend using a hard drive as well. You can partition a hard drive so that one part is just dedicated to the time machine back up. 
https://support.apple.com/guide/mac-help/back-up-files-mh35860/15.0/mac/15.0

Yea, I think the VM is a good first step. I know its a lot to go out and buy a whole new computer for something you're not even sure how to use yet. I think with familiarity it will hopefully make things easier! 

 very nice of you to tell me all of these.
I have this mac for 3-4 years.  Never even looked up what time machine is 😅
I will set up time-machine and will try Linux....😀