More info and examples at http://getbootstrap.com/css/#grid

Stacked-to-horizontal

.col-md-1
.col-md-1
.col-md-1
.col-md-1
.col-md-1
.col-md-1
.col-md-1
.col-md-1
.col-md-1
.col-md-1
.col-md-1
.col-md-1
.col-md-8
.col-md-4
.col-md-4
.col-md-4
.col-md-4
.col-md-6
.col-md-6

Mobile and desktop

.col-xs-12 .col-md-8
.col-xs-6 .col-md-4
.col-xs-6 .col-md-4
.col-xs-6 .col-md-4
.col-xs-6 .col-md-4
.col-xs-6
.col-xs-6

Mobile, tablet, desktops

.col-xs-12 .col-sm-6 .col-md-8
.col-xs-6 .col-md-4
.col-xs-6 .col-sm-4
.col-xs-6 .col-sm-4
.col-xs-6 .col-sm-4

Responsive column resets

.col-xs-6 .col-sm-3
Resize your viewport or check it out on your phone for an example.
.col-xs-6 .col-sm-3
.col-xs-6 .col-sm-3
.col-xs-6 .col-sm-3

Offsetting columns

.col-md-4
.col-md-4 .col-md-offset-4
.col-md-3 .col-md-offset-3
.col-md-3 .col-md-offset-3
.col-md-6 .col-md-offset-3

Nesting columns

Level 1: .col-md-9
Level 2: .col-md-6
Level 2: .col-md-6

Column ordering

.col-md-9 .col-md-push-3
.col-md-3 .col-md-pull-9