If you wish to implement the contact page like in our demo you can do it this way
+ Go admin site -> Main Menu -> Contact Us menu item
Menu Item Type: Contact company
Select Contact: any
+ Go Contact Us component and find Select contact choose with Menu item in Menu
Input all info
In Display tabs -> Display format: Plain
With the 404 error page, you can create that page like as our demo.
+ Go Article Manager in Content -> Create 404 Page article with a contain
<div class="well" style="font-size: 13px; font-weight: 400;"><center>Each <strong>JA Joomla Template</strong> has its own matching 404 page. Below is the screenshot of <strong>404 page style</strong>.</center></div>
<p><img src="images/joomlart/demo/404.png" alt="" /></p>
+ Go to Admin site -> Create 404 Page from Menu
Menu Item Type: Single Article
Select Article: 404 Page from Article
For more info, you can reference this guide: http://docs.joomla.org/Creating_a_Custom_404_Error_Page