Polarization is giving a wave a certain direction or orientation.
When dealing with polarizing light, we can think of a light wave as a folded paper plane.
It has a tip, a bottom fold, a left wing, and a right wing. You can point it any direction, but it will always have the same "shape"
Light waves are very similar: they have electric fields in one direction, and magnetic fields in the other (like a cross or arrow).
Normally, the light we get from the sun is pointed in random directions.
When we polarize light, we make light point some direction
There's much more to the how, why, and what of polarization, but I hope this helped out! For further reading, check out the wikipedia page: Polarization of waves