Adding New Column not Working

I am a newbie to Web Programming so basically i only know HTML/CSS just learning JS.
When i add a new column then i loose all the formatting.
So it comes with 5 columns, how do we add more?

<thead>
<tr class="test">
<th >Vendor</th>
<th >Product</th>
<th >Description</th>
<th >Cost</th>
<th >Cost</th>
<th >Error!!!!</th> <!-- Looses format once i add this th -->
</tr>
</thead>

Here is the link to the example

http://live.datatables.net/avufik