You seem to be using a terminal on a smartphone. Not sure if that makes any difference with your school problem, or if it is correctly emulating a Linux filesystem. I would recommend going through the entire lesson from the beginning to reinforce the concepts it is teaching you... which is filesystem structure, and how to navigate within the filesystem and move files from one place to another.
To start... look carefully at your error. It does not say anything about /root. It is specifically talking about /tmp. Again, thinking about this carefully.... /my_school/tmp is NOT the same location in the filesystem as /tmp.
As
@captain-sensible is telling you, you need
mkdir
to create /tmp... or so it seems from your error report. Or if /tmp already exists, you are not using it. Try
ls /tmp
to see if there are any files already there.