The strength of the radio waves copy the sound vibrations. The detector changes the back and forth radio wave electricity into one way sound electricity. When the radio wave is strong, it makes strong sound electricity. When the radio wave is weak, it makes weak sound electricity. This makes sound electricity that copies the sound vibrations.
Normal wires let electricity flow both ways.
When radio first started, inventors found rocks that work for detectors. They were crystal rocks, like galena, pyrite and lots of others. That is where the name Crystal Radio came from. Now detectors are made with wires on them. Engineers call them diodes.