Here is a YouTube video about Intro to the FFT or Fast Fourier Transform, and is part of a growing collection of videos I have found to be useful. The reason is see good visuals on what the FFT is and how it works in analyzing or processing signals and understanding science related to software defined radio.
This tutorial, "Intro to the FFT or Fast Fourier Transform" is free education you can watch, which will help you deepen your knowledge and be better prepared for licence exams, schoolwork, or operating radio equipment.