In a parent template called 'parent.html', blocks are included like so:

{% block block_name %}
BASIC CONTENT GOES HERE
{% endblock %}

To utilize the parent template in another template, use the following syntax:

{% extends parent.html %}

{% block block_name %}
NEW, CHANGED CONTENT GOES HERE
{% endblock %}

Note that the 'extends' block must be the first thing in the child template.