The human brain has a penchant for identifying patterns, decoding them, then recoding them for later reuse. Not only does this cycle make it easier for us to understand the world around us, but it helps us constantly improve the tools we use to interact with it. Perhaps one of the most salient manifestions of this in the design world are grids.
Grid-based layouts stood the test of time—they predate both print and movable type—and are now a staple of modern Web design; the sheer number of tools, resources, and frameworks testifies that. This very abundance, however, makes it challenging to get started with grids, especially without proper understanding of the problems they are meant to solve.
A grid is a tool that can be used to establish a spacial hierarchy of the content. It can be fixed or fluid, horizontal or vertical, uniform or responsive. Grids should be viewed as guides, not boundaries; good designers know how to use grids, great designers know how and when to break them.