how to reinstall catalina on a MacBook Pro (Retina, 15-inch, Mid 2015)

I wish it were that easy. I have a Macbook pro (15 inch retina display mid 2012) I planned on giving it to my sister in-law.

First I clean (erased) the Hard Drive (actually internal ssd). Then tried to do the "reinstall". Since the HD was completely

wiped, I had to do an Internet reinstall. I was stopped in my tracks with the message "Can't download the additional

components needed to install Mac OS X". Some people had trouble with Internet connections in this Forum - I had

absolutely no trouble with Internet connection. Nobody seems to address the above error message problem.

BTW, I was trying to install "mac OS X Lion", I did not have any other option choice. I later downloaded Catalina .dmg file

(4.5GB), but do not know what to do with it. Thanks in advance, Doug