This is pretty simple to do. This is covered in the 2nd tutorial so you might want to read that http://doc.silverstripe.com/doku.php?id=tutorial:2-extending-a-basic-site . Basically you need to do 2 things. I am going to assume you have your holder/news page types the same as Tutorial 2.
So step 1 Make the function that gets the latest news. Add this to the class Page_controller in Page.php.
function LatestNews() {
$news = DataObject::get("ArticlePage", "", "Date DESC", "", 3) ;
return ($news) ? $news : false;
}
One that you have that function you need to output the news list on the website. So you need to add some code like this to where ever you want to out put the latest news -
<ul id="NewsList">
<% control LatestNews %>
<li><a href="$Link" title="Read more on "{$Title}"">$Title</a></li>
<% end_control %>
</ul>