Vector3
As you know Unity a bit, have you heard of Vector3 already? If you haven't, I will explain it very briefly. Vector3 represents a 3D vector and a point or direction. The Unity documentation says:
"This structure is used throughout Unity to pass 3D positions and directions around. It also contains functions for doing common vector operations."
Feel free to study more about Vector3 at this link: http://docs.unity3d.com/ScriptReference/Vector3.html. If you are not a math master, you will feel confused now. All I want you to remember right now is that Vector3 can be used to store the position of a game object in 3D space. It contains the X, Y, and Z positions in 3D space. That's it! Don't bother yourself with too much information about 3D vectors at this stage; it is a massive subject.
Line 39 is where we are creating a new Vector3 type variable to store the position we will move our level position to in the next few lines.
Note
You can use List<T>.Count
to access the current size of...