Can someone explain Shortselling to me?

Okay so I am taking an investments class in school right now and we were talking about short-selling. I understand that you basically borrow stocks and sell them immediately betting that the stock price will go down.  Then you buy them once they go down? How does this make you money?

Can someone please simplify this to me, I just don't understand this concept.  I hear Mark Cuban is famous for this and you can make a ton of money by doing this in a bear market.

Sell short AMZN at 60 bucks

Stock goes down and you buy it back at a lower price-

Buy to cover AMZN at 40 bucks

Net result is a gain of 20 points.

You sell shares you dont own at a price you think will go lower and buy it when they go lower and profit from the drop in price.

Okay, but how exactly do you profit by the price going down 20 points?
I'm not sure what "buy to cover" means, maybe that's why I don't understand this concept.

Think of the trade BACKWARDS.

Short selling means sell first, buy later.

Buy to cover just is the term used in short selling, you sell SHORT, or sort of like digging a hole since you dont own the shares and you COVER that hole when you buy them back.

Buying to cover only means finalizing a short sell, the buy transaction.

Ok It now makes sense to me. I was not thinking of it in the backwards form which is why I was not understand how you made money.  Thanks for the help guys.