Apple Users

From stackexchange (short version)
How can I open an app using Terminal
http://apple.stackexchange.com/questions/355037/ddg#355040

You can use open’s -a option:

open -a Mail

You can specify the application path instead:

open /Applications/Mail.app

(cool applescript not shown)
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Apps in the /Applications directory seem to work fine. (I don't know if anything in your $PATH will do so as well)

A bit more here (with pictures)
https://www.wikihow.com/Open-Applications-Using-Terminal-on-Mac

and more than you ever wanted to know, ever:
>man open

GOOD LUCK.

_____
Now, here's the secret sauce: an application is a DIRECTORY. But behaves like a file.
You can look at an app in the finder and right click/control click "Show Package Contents" to explore, but please don't change anything!

And P.S., you can "cd" to anywhere on the file system, and in the terminal that got you there
"open ." and that opens a finder window.