Installation on Ubuntu-Mate OS, iMac Hardware

I have downloaded the AppImage and on the second or third attempt I got it to run (with permission in a terminal window). So far, so good.
Then the Handbook (https://musescore.org/en/handbook/3/install-linux#AppImage-install) advises me to Install it. This involves "To install it, run the AppImage from the Terminal with the "install" option (see immediately below). "
We go to
Using command line options
where we read "You will need to change directory (cd) to wherever the AppImage is saved in your system, for example:

cd ~/Desktop
./MuseScore*.AppImage [option...]" 

Note that the square brackets are shown in purple. Why?
Okay, I've typed that into the terminal window (but the square brackets are just in black and white).
It doesn't work.
Then I've typed it in again, putting the word "install" (without the quotation marks) (and without the three fullstops) inside the square brackets. Again, it doesn't work.
I have tried to follow the instructions EXACTLY.
Why don't they work?
Can anyone please help me to overcome the problem with wrong instructions on the webpage?
So, what do I do next, please?