Amazon sales rank and other mysteries

So, authors have a strong opinion about Amazon. Through details that I don't quite understand, but involve discounted prices, books sold on Amazon don't pay as much to authors (unless you self publish). And it's best to support independent bookstores, which live in a community and nourish that place. HOWEVER. People are not going to stop buying on Amazon. It's simple and easy. It is almost the first question people ask when they want to buy my book. Amazon is not going away--and speaking as one who tries to buy books in her local store, but as one who also lives far, far away from most retail, there are times when I buy things on Amazon. They just aren't available within 100 miles (melatonin, more than 3 mg, for example). 

I really, really don't read reviews of my books, as I have mentioned before, unless people tell me I should for content. I mean, I'm not going to change anything now--you don't get a do over. I mistakenly stumbled across one for Geography of Water and when I saw the title "A Respectable First Attempt", I decided I didn't need to read further. For writers, the reviews that matter are before you publish the book. You can drive yourself nuts, like when a friend reviews your book on a site and only gives it four stars. FOUR STARS WHY?! WHY NOT FIVE? You see the trouble you can get in.

But, I keep hearing about Fire in the Heart popping up in different places. New York! Portland! Norway! So I snuck on Amazon, half covering my eyes, to see I had 8 five star reviews! Wow! And even better, the sales rank figures:

Now, I don't know really what this means.  I read an article on it and still don't quite get it. And honestly, "professionals and academics"? Am I really one of those? You know, this might fall strongly in the "I don't care, I don't want to know, I just like the numbers" category. Living in ignorance is all right with me!