How "exactly" does sway/strut bars work for suspension on a car.?

my friend just got strut/sway bars and i can't see what its supposed to do. my friend says it keeps the frame of the car from "slightly" bending when taking turns hard, but i'm thinking "the frame of the car (reinforced steel) is bending?" this already sounds wierd and if it is true, how does a little aluminum bar keep that from happening. im looking at this strut/sway bar (under the hood) and i can't grasp the concept of what it is supposed to do or how it would make a difference. i know it must do something (im not saying im right and everyone else is wrong) i just would like to understand fully what it does and how. thanks for any feedback.