If what you are after here is to rotate the cube when you are holding down Fire1 button and moving the mouse scrollwheel up/down (which is what this flowscript does), then you will need to use the Y value of the Vector2 rather than the X. The x delta for the mouse scroll is always 0.
Remember, that what you have created in the image, requires that you are holding down the Fire1 button (which by default in Unity is left mouse click or the control key). Otherwise the Rotate node will not execute.
When I hold down the left button and move the mouse nothing shows in the mouse delta.I thought that mouse delta showed the movement of the mouse from one frame to the next.Do I have to use the scroll wheel?
Input.mouseScrollDelta is the mouse wheel delta, not the mouse position delta.
While you could manually calculate the delta from Input.mousePosition, here is a easier way to do what I assume you want:
In the event node used here “Input Axis(Custom)”, you can define any custom axis to use which is set in “Project Settings/Input Manager”. By default Unity has a lot of them already created. “Mouse X” and “Mouse Y” are basically the values you are looking for (mouse position delta).
For your convenience here is the Input Axis inspector:
You can add any number of axis you want to get their value. The “Out” flow port is called when either of those axis is not zero.
Can you just collect all these small examples that you did over and over for all kinds of tasks and upload a .zip to the downloads area? That way we would have a library to look up how stuff can be done. This is really missing.