How do I set the number of columns each region ?

How do I set the number of columns each region ? And for elements?

I've tried to uncomment @import "960/grid"; and call a @grid mixin:

.view-benefits .views-field-edit-node { 
	float:left; 
	@include grid(6);
}

But nothing happended except errors.
Please advise.

Thanks

Amnon