Those 3 column thing shown in demo are Text Widgets used in Front Page Widget Areas. Simply go to Appearance → Widgets, drag one Text Widget into Front Page Widget Areas, give the text widget a name (will be used as Title of that area), and then put this code below into Text Widget content.
<a href="https://selademo.wordpress.com/page-templates/full-width-page/">
<img src="https://selademo.files.wordpress.com/2014/08/mg_9371-1.jpg">
</a>
<p>
This is a full-width page template. It’s great for embedding a map, a large video, or a contact form.
<a href="https://selademo.wordpress.com/page-templates/full-width-page/">Read more →</a>
</p>
Change all the links to yours, link to your page, link to your image (upload image to your WP site first and get the image link), change the paragraph to your own. Repeat the steps for the other two.