Greetings, Porteno.
Assuming we haven't answered your question yet...

It seems you have a working Knoppix 7.0.4 DVD-size LiveCD (or USB).
The fact that you can boot up and get a good answer to testcd or testdvd
means that 99% of the iso is ok.

An md5sum test would assure you of the last 1%. You need a 'command line'
to do this test. If you have a working Knoppix, then you can see it has a
graphics user interface.

Some of the seemingly arcane advice you've been getting assumes you will
'call up a terminal' and do a few 'command line' things. Where is the
command line on Knoppix? The terminal on Knoppix is simulated by the program
lxterminal which you can access from your task bar or from the main menu,
under accessories.

A useful command is man. Try man md5sum, for example. After that see if
some of the advice makes more sense.

Hope this helps.