Here is a YouTube video about Complex Numbers and Discrete Fourier Transforms, and is part of a growing collection of videos I have found to be useful. The reason is why use complex numbers to represent different things in the context of physics, signal processing, and software defined radio and understanding science related to software defined radio.
This tutorial, "Complex Numbers and Discrete Fourier Transforms" 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.