The red and blue arrows represent two complex numbers, namely those whose plot puts them at the tip of the arrows. You can change these as you please either by left clicking on the arrow heads and moving them, or by entering new values in the boxes on the left, over the red and blue entries respectively.
If you enter them that second way, you should clock on ‘plot‘ afterward. The range shown in the plot can be altered by entering those you wish, where appropriate.

IF you select one of the combinations below these, by clicking on the adjacent box, you will see that combination of those two numbers. Once chosen, you can move either of the numbers, and watch how that combination changes as that number changes. If you choose one of the functions in the list on the bottom, you must click on plot to get the right picture.

This tool uses JQWidgets extensively. Please verify their copyright.

Developed by Daniel Kleitman and Jean-Michel Claus.