I used to point my 35mm with polorizer at a window, and turn the filter ring till the glar on the window dispersal.Yes, you need to look through the filter and rotate to get the best results..which will vary as the MM rotates in relation to the sun. There is a 90 degree rule that can help set the polarizing filters for good all around, but not optimum results.
I have the Tiffen set, and I don’t think there’s an “on or off”....if they are like other polarizing filters, it all depends on the angle of the light