Get three columns starting at desktops and scaling to large desktops of various widths. Remember, grid columns should add up to twelve for a single horizontal block. More than that, and columns start stacking no matter the viewport.
Get two columns starting at desktops and scaling to large desktops.
No grid classes are necessary for full-width elements.
Per the documentation, nesting is easy—just put a row of columns within an existing column. This gives you two columns starting at desktops and scaling to large desktops, with another two (equal widths) within the larger column.
At mobile device sizes, tablets and down, these columns and their nested columns will stack.
The Bootstrap 3 grid system has four tiers of classes: xs (phones), sm (tablets), md (desktops), and lg (larger desktops). You can use nearly any combination of these classes to create more dynamic and flexible layouts.
Each tier of classes scales up, meaning if you plan on setting the same widths for xs and sm, you only need to specify xs.
Clear floats at specific breakpoints to prevent awkward wrapping with uneven content.
Reset offsets, pushes, and pulls at specific breakpoints.