Hi Nicholas, Thank you for your great guidance!
I finally solved the problem as you mentioned.
One tricky thing is that the last command of "pkg load symbolic".
When I ran it at dos prompt of octave and it did not work.
But soon after I ran it at command window of Octave (GNU), then
it worked!
How i can clarify this kind of sensitive matter correctly?
1. please explain what you mean by "dos prompt of octave" and "command window of octave"
I assume since you are running Windows, that you run octave by double clicking one of the Octave icons created when the program was installed. The installer will create two icons, one will start only the Octave command line (also called the interpreter. it looks like a Windows command line or Dos prompt, but it is within the Octave program). the other icon will start the Octave Graphical Interface. This also has the same Octave command line (interpreter) window, but with other graphical elements around it. On the left side is a directory or folder tree and a variable list.
2. once the package is installed, the "pkg load symbolic" command should work in the Octave interpreter window from any directory. Only when manually installing a package ( pkg install symbolic-x.y.z.tar.gz) do you need to make sure that Octave can see the file by being in the same directory. You can do this with the CD command, as you had said, or you can use the folder tree in the upper left of the graphical interface.
Now that you have it working, I would suggest practicing a simple set of instructions for the students to follow if they must also install the package.