An ohmmeter is a device that measures the resistance of a circuit or a part (remember that resistance is measured in ohms). Most ohmmeters have a meter or LED display to indicate the resistance. This Project is a bit different, it lets you hear the difference in resistance between various parts.
This Project is actually a version of the audio oscillator see Oscillator Section circuit we've used in many other Projects. When a resistance is connected across the two long wires it provides negative feedback so the circuit can oscillate.
After you finish the wiring connections, turn power ON. Measure the resistance of several different resistors. What differences in sound do you notice when you measure different value resistors?
Is there a pattern to these changes? (You'll probably find it helpful here to review the notes you've made on audio oscillator Projects.)
Try touching the end of the two long wire together. What do you hear now from the Speaker? Can you explain why this happens? (Again, you'll find it helpful to check the notes you made on earlier Projects.)