Are you familiar with HTML and CSS at all?
It's very common for a set of links, such as navigation links, to be marked up as a list because that's basically what they are - a list of links. So you'd start with something like
<li><a href="page1.html">First Page</a></li>
<li><a href="page2.html">Second Page</a></li>
<li><a href="page3.html">Third Page</a></li>
<li><a href="page4.html">Fourth Page</a></li>
Then you use CSS to control the layout and styling of these links.
If you visit the page in your link, and right-click on one of the buttons, your browser should show you a menu option of "Inspect element", or something similar. If you select that, you can see both the HTML code in use and the styles being applied to it.