At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga.
Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus.
Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
As you hopefully know, we can think of light as a wave. Ordinary light, such as from the sun, is unpolarized. This means that the waves are oriented in all directions around the axis in which the light is traveling. That's the light at the left of this picture.
Polarized light, by contrast, has the waves all oscillating in one direction. You can see in the diagram how the unpolarized light passes through a filter which selects for just the light oscillating in the vertical direction.
The last filter in the diagram selects for light waves oscillating horizontally. As there are no more such light waves, that second filter stops the vertically polarized light.
Not the answer you are looking for? Search for more explanations.
Light reflecting off horizontal surfaces are often horizontally polarized. If you want to reduce road glare when you're driving, we often wear sun glasses that have a polarizer in the vertical direction which filter out the horizontal light.
See this diagram.