Can anyone help explain this solution to determining a graph is non planar

Question

Im a bit confused about the solution to this,

It shows a graph, and then explains why the graph is not planar, by showing a $K_{3,3} minor $

So can anyone help explain what is going on in this picture?

Thanks

Answer 1

Each blue ellipse is a "left vertex" of $K_{3,3}$ and each green ellipse is a "right vertex" of the same graph. The edges covered by the ellipses are contracted to give the minor and the top vertex of the star is simply omitted.