A cathode ray oscilliscope is simply a device which plots sound and i think maybe other waves, using a microphone. your teacher should hv done a prac which shows u one, if as i imagine u are doing the prelim physics course
isn't that the machine that measures different wave lengths, the frequency and so on? you create a sound by like hitting a table or something then on the screen it shows the sound waves..
it's kinda like those machines that measure heart beats :d