 We use the Fourier transform to tell us what a signal is built out of. Just as this car can be built out of individual Lego bricks, so a signal can be built out of individual sinusoids. Once you know which sinusoids your signal is built out of, there is no end to what you can do with that information. For example, here's a signal. And here are all the sinusoids the Fourier transform found in the signal. Too many sinusoids! But most of these sinusoids are small compared to bigger sinusoids at nearby frequencies. What if I remove the smaller ones? It sounds the same. This is how MP3 compression works by locating and removing frequencies that our ears cannot detect. And this is only one use of the Fourier transform. Want to find out how the Fourier transform works? Check out my channel.