If z = x + iy is a complex number, it can be represented by a point (x, y) on the Argand plane. Take two mutually perpendicular straight lines XOX' and YOY'.
Now plot a point whose x and y coordinates are the real & imaginary parts of z.
This point P(x,y) represents the complex number z = x + iy.
For exp. the point (6,2) in an Argand plane represents a complex number z = 6 + 2i.
The point (3, -5) in an Argand plane represents a complex number z = 3 - 5i