Hello again from the CLI novice!

Vimtutor is fun, if confusing on one section. I was unclear on the directions about editing a file. Were we supposed to input our own file to edit? I rather dumbly tried it with a file called shutdown (not a good choice, in hindsight) that I had just created to remind me of how to shut down. I pressed enter ended up with no command prompt and little more than the word VISUAL on the screen. I had to restart my virtual machine.

Now some questions: Is there a comprehensive list of commands. Or are they being added to all the time and thus make it impossible to include all of them in one place?

More command questions: How is it that Linux responds to these commands? Are the commands designated in a list, in a text file preloaded into all Linux systems, that can be added to at any time by accessing and resaving that text file?

From a LIS perspective it seems problematic that Linux stores everything in one great directory. Can subdirectories exist to at least group files/directories together temporarily?

Finally, I'm a little shocked by the Linux vocabulary, when you have to "mount" before you "insert" and "unmount" before you remove. To be at this climbing level of technology and then stumble over cro-magnon terminology is disturbing. Of course, if there is an alternative metaphorical scheme behind the mounting thing, please enlighten me, and I will duly retract.