3.30 describe an experiment using an oscilloscope to determine the frequency of a sound wave

Have an noise made into a microphone attached to an oscilloscope, for example have someone try to sing a note. See how many oscillations there are per second, this will be your frequency. Try changing the pitch of the note and see it the number of oscillations per second changes.

An oscillation is the completion of one wave i.e from one peak and the next.