This video presents an introductory tutorial on IQ signals - their definition, and some of the ways that they are used to both create / generate modulated RF signals, and demodulate / analyze RF signals.  IQ signals are most often used in the transmit and receive paths of Software Define Radios (SDR).  A PDF of the drawings can be found here:
http://www.qsl.net/w/w2aew//youtube/Basics_IQ_signals_modulation.pdf
Here's a recent blog post (not mine) that also explains this quite clearly:
https://blog.aunyks.com/2020/11/understanding-complex-signals