launch YouTube from the command line
Solution 1:
You can install Freetube, a privacy friendly youtube client, and launch it with the command freetube.
Alternatively, you can open YouTube with Firefox, with the command
firefox https://youtube.com
For assigning keyboard shortcuts to a command, see this webpage.
Solution 2:
Depending on what exactly you want, it can be as simple as
xdg-open https://www.youtube.com
which will start your default web browser with that URL; or open a new tab in a browser instance that is already open.