Before start learning about Flexible Grid System, you need knowledge about Grid System and Responsive Design.
<meta name="viewport" content="width=device-width, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no">
By switching to compile view, you can examine the CSS properties of classes and mixins. Knowledge about this topic will help to improve your abilities.
On CSS; static section, on Sass, Less or Stylus, dynamic sections are marked as @variable.
For browser compatibility requirements -ms, -moz and -webkit aren't added to the samples.
Dynamic (Compilation Tool)