On google it says to multiply the Orange Side with the Green Side, it gives me a hugenumber/length of 607, showned below by the dark blue side/length in the picture.
How can I use this length for it to tell how two Vectors compare to each other?
Wikipedia has a decent article on it. The dot product or scalar product comes from multi-variable calculus, and is related to the Law of Cosines. The way that you are doing it is incorrect. The dot product works on vectors only such that
where the vector is <a1, b1>, <a2, b2>, etc… So consider two vectors <2, 4> and <5, 7>. Using the above formula, we end up with
2x4 + 5x7 = 8 + 35 = 43
So the scalar product of the two vectors is 43.
The other product (cross product, vector product) returns a vector that is orthogonal to the two given vectors. It’s useful for projecting into 3D space from a surface.