Simply include Flex in the <head> like any other CSS file.
<link rel="stylesheet" type="text/css" href="flex.css">
Apply the .grid class to a div and nest your .row and .column(s) elements inside.
Notice the use of the .alpha and .omega classes on the first and last elements.
<div class="grid">
<div class="four columns alpha">Element 1</div>
<div class="four columns">Element 2</div>
<div class="four columns omega">Element 3</div>
</div>
Renders
<div class="grid">
<div class="three columns alpha">Element 1</div>
<div class="three columns">Element 2</div>
<div class="three columns offset-by-three omega">Element 3</div>
</div>
Renders
<div class="grid no-gutter">
<div class="four columns alpha">Element 1</div>
<div class="four columns">Element 2</div>
<div class="four columns omega">Element 3</div>
</div>
Renders
Be sure to define your smallest size with "sm-"! Failing to do so will break your grids on smaller devices.
<div class="grid">
<div class="sm-six columns">Element 1</div>
<div class="sm-six columns">Element 2</div>
</div>
Renders
<div class="grid">
<div class="sm-twelve md-three columns">Element 1</div>
<div class="sm-twelve md-three md-offset-by-three columns">Element 2</div>
<div class="sm-twelve md-three columns">Element 3</div>
</div>
Renders
<div class="grid sm-six lg-three xlg-four">
<div class="parent">Element 1</div>
<div class="parent">Element 2</div>
<div class="parent">Element 3</div>
</div>
Renders
<div class="grid three">
<div class="parent alpha">Element 1</div>
<div class="parent">Element 2</div>
<div class="parent">Element 3</div>
<div class="parent omega">Element 4</div>
</div>
Renders
<div class="grid">
<div class="three columns alpha">
3 Cols <br>
<div class="six columns alpha">6 Cols</div>
<div class="six columns omega">6 Cols</div>
</div>
<div class="three columns">3 Cols</div>
<div class="three columns offset-by-three omega">3 Cols - Offset 3 Cols</div>
</div>
and it renders