Vector class explanation

Hey all, 

I need an explanation of Vectors in WPF. I just don't understand how is a vector defined here. In math, vectors have a direction (can be determined by angle) and value. In picture, here it is:

Could someone please explain me how this:

Vector vec = new Vector(10,10);
vec.Length // what is this???

looks like? And how to use it?

Please, in picture.

Knowledge: C, C++, C#, Java, Pawn