The best way this was explained to me was instead of using a number line, imagine numbers more as a graph where you have an x and a y axis. The c axis is all the regular numbers we normally use, and the y are numbers that we don’t yet have names for and hence called them “imaginary”. But they both still intersect at 0, and the “distance” between them would be the same for regular numbers, so it’s handy to invent a nomenclature for turning the axis 90 degrees, so i.