Attach to lens, point camera at a reflective surface such as a glass table top ( NOT a mirror ok? )
Then turn the CPL filter and see the reflection appear and disappear. Or you can point the thing to the sky and turn. See how the blue 'changes'. Very simple. :sweat:
why buy something when you don't know how to use it? :think:
choose a sunny day, face 90 degrees to the sun, point to either the blue sky & clouds (not overcast!!) or foliage. With the CPL in hand, slowly slowly rotate the outer ring. Slowly because the saturation change is very slight to the naked eye, chances are that you'll miss it since you don't know what to look for. The saturation change comes and goes, so sooner or later (before the eyes tired) you'll notice some difference.
Better yet, shoot some pics with and without it. Follow the 90 degree rule for best effect.