It is an instrument that measures voltage against time. This is known as frequency. If the trace takes one second to transverse the tube face (adjusted by the "x" control) and the input to the "Y" amplifier varies from say +2volts to -2volts and it did this + & - variation at 4Hz then a square wave will be shown on the tube face, which will be repeated four times. If the frequency is doubled then eight repeats will be shown. As the osilloscope has variable "x" frequency and the "y" amplifier gain can also be varied then any waveform can be measured. All 'scopes work in basically the same way but some are more complicated to use than others. I do hope this is of help but do ask me if you need any further assistance and I will try to help.