Polar Form and Rectangular Form Notation for Complex Numbers. (n.d.). All About Circuits. https://www.allaboutcircuits.com/textbook/alternating-current/chpt-2/polar-rectangular-notation/Links to an external site. Rectangular notation  denotes a complex number in terms of its horizontal and vertical  dimensions. So 4+J4 could also be said as 4 Right and 4 up on a graph.  The first 4 is your real number and the J4 is the imaginary number. I  liked this website because it walks through the basics and builds on  that, for both polar form and rectangular form. 

Johnson, L. (2019, March 2). How to Use a Coordinate Plane in Real Life. Sciencing. https://sciencing.com/use-coordinate-plane-real-life-8743000.htmlLinks to an external site.  I like this site because it gives real world examples of how these  numbers are used. Calculating waveforms in AC electricity is the first  example that stood out to me as something that I could actually  understand.