In a normal $2D$ graph the $y$-axis represent the height, $x$-axis the weight. When we want to refer to a certain point on the graph we say $(x, y)$. With complex numbers the case is different, have a look at this graph:
We have now imaginary axis and real axis and that make sense. I however don't understand why points are written like $(1+2i)$? Adding these two points together means that we are converting this $2D$ graph into a $1D$. Why not write them like $(1, 2i)$ instead?