Hi. I had problems using the basic instructions on the lecture, as well as the (excellent) info in the QA.
I was able to get Android debugging working only after I loaded the correct USB driver.
There’s an excellent guide here:
https://developer.android.com/studio/run/oem-usb.html#Drivers
For me (Samsung Note Edge) I had to navigate through Sansung’s menus (which wasn’t easy as the model number is decorated with additional fields, but I figured it out), and had to download the “USB” driver. It won’t say “Developer” and the web page is pretty bare. I eventually figured out there was only one and that must be it 
just look for “USB” under downloads and you’ll get it (if you have a Samsung). The link, above, which has a link to all phone drivers, was OK and got me there although I did have to search on Samsung’s site (it’s under support):
However, follow the first note to get ALL the drivers (unless you also have a Verizon Note Edge, lol).
== John ==