The Finstall script creates the ferret_paths.csh and ferret_paths.sh shell scripts. Before attempting to run ferret (or pyferret), you need to "source" one of these scripts to setup the environment variables needed by ferret as well as make the ferret executables (or pyferret script) discoverable (add the directory to the PATH environment variable).
There is another obsolete database program called ferret that has nothing to do with us, is what Ubuntu is referring to with its message about using "sudo apt --install", and what your student temporarily installed. (There is no version 0.6 of our ferret.)
I suspect your installation of our Ferret (or PyFerret) program was successful and the only step you were missing was to "source" the ferret_paths script. So for Bourne shells (such as bash), you use the "." (dot) command with ferret_paths.sh:
$ . /path/to/ferret_paths.sh
For C shells (such as tcsh), you use the "source" command with ferret_paths.csh
% source /path/to/ferret_paths.csh
To check that ferret (or pyferret) can now be found, the command "which ferret" (or "which pyferret") should return the location of the ferret executable (or pyferret script). If this is the case, then you can run ferret (or pyferret) by just entering "ferret" (or "pyferret") at the command line prompt.