first things first.... This is just an assumption that is a number that exists and is usually represented as "i" or "j".
Any multiple of is an "imaginary number" - eg is an imaginary number.
A number which is (or can be ) simplified to the form: is a "complex number" eg is a complex number.
a is the real part.
b is the imaginary part.
Complex numbers can be represented on a graph which is called an "Argand Diagram".
[Can't draw graphs here so please bear.]
Remind your self of the cartesian coordinates... (x, y)
To exactly define a point on the graph, you need to have to numbers: x and y coordinate.
Likewise a complex number can be represented as a point on the argand diagram. By convention, the real part is the horizontal distance from the origin (like x coordinate on cartesian) and the (fake...err..) imaginary…