Once you have created the number of columns you need, you now need to create the number of rows. Unlike columns, rows aren't restricted by area and you can create as many as you need. You do this by copying and pasting your finished code as shown below, until you have the number of rows required. The code below is what I used to create the example grid. The beauty of using the div element is you can always add extra rows in the future if required.

<div class="columns">

 <div class="column"></div>

 <div class="column"></div>

 <div class="column"></div>

 <div class="column"></div>

</div>

<div class="columns">

 <div class="column"></div>

 <div class="column"></div>

 <div class="column"></div>

 <div class="column"></div>

 <div class="column"></div>