Silverstripe HTML Blocks

Allows to inject HTML Blocks into .SS templates and HTMLContent as shortcode (TODO)., _(*1)

<% if $HTMLBlockExist('social-links') %>
    {$HTMLBlock('social-links')} <%-- you can manage this HTML part from the admin panel now --%>
<% else %>
    <ul>
        <li><a href="https://en-gb.facebook.com/openhouselondon2017" target="_blank" class="social">Facebook</a></li>
        <li><a href="https://twitter.com/openhouselondon" target="_blank" class="social">Twitter</a></li>
        <li><a href="https://www.instagram.com/openhouselondon/" target="_blank" class="social">Instagram</a></li>
    </ul>
<% end_if %>

how to use HTML Blocks 1 , _(*2)