How do I make it so if a box turns upside-down then it will display a message??
The rotation is stored in the transform of the box, create a script that checks the rotation and if it falls within your defined parameters then display a message.
Hopefully you will see what I mean if you add a box to your scene - then rotate it… but keep an eye on the transform details in the inspector.
You might benefit from trying out the free tutorials/examples at unity3dstudent.com
Just as a side note, making these sorts of determinations based on Euler angle values can be a little iffy due to aliasing. If you want to determine when the box has been turned upside-down (for some definition of ‘upside-down’) relative to its initial orientation, I’d recommend instead looking at its local ‘up’ vector. (A simple test would be to see if the y coordinate of the local up vector is below some negative value, e.g. -.75.)