xs (for phones - screens less than 768px wide)
sm (for tablets - screens equal to or greater than 768px wide)
md (for small laptops - screens equal to or greater than 992px wide)
lg (for laptops and desktops - screens equal to or greater than 1200px wide)

Hello World!

Resize the browser window to see the effect.

The columns will automatically stack on top of each other when the screen is less than 768px wide.

.col-sm-4

.col-sm-4

.col-sm-4

.col-md-4

.col-md-4

.col-md-4

.col-lg-4

.col-lg-4

.col-lg-4

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.