Okay kiddo, so a Fessenden oscillator is a gadget that makes radio waves. Do you know what radio waves are? They're invisible waves that go through the air and carry information like music, voices or even pictures.
So, the Fessenden oscillator was invented by a man named Reginald Fessenden. He made it to send radio waves through the air so people could talk over long distances without using anything like a phone or a computer.
The oscillator works by taking electricity from a power source and sending it through a special crystal called a "piezoelectric crystal." This crystal creates tiny vibrations that make electric waves at a very high frequency - this is how we get the radio waves.
These waves are transmitted using an antenna (which is like a tall tower) to send the waves through the air to other antennas that can pick them up. And that's how we can listen to the radio today!
Pretty cool, huh?