A polariser works with ambient light therefore your best trying it outside,i think looking at your computer probably wont be bright enough to see any discernable difference.
Stick it on your camera and look thorugh the viewfinder and point it at the sky (obviously not directly at the sun LOL) now turn the filter whilst still looking throught the VF and you should now see the difference as you turn it.
HNCP37, HNCP42 Circular Polarizer Filter, HNCP CP Polarizer Display
Have a read of this....
HAHA back again for an edit just been outside and realised i forgot to say not a blank sky as there will be no detail to reflect any light so you wont see anything...LOL