Jekyll uses a templating language called liquid, take a look at this crash course

This code should generate a list of posts. You can also see the code for this post here

{% raw %}

<ul>
  {% for post in site.posts %}
    <li>
      <a href="{{ post.url }}">{{ post.title }}</a><BR>
      post.excerpt: {{ post.excerpt }}<br>
      post.tags: {{ post.tags }}<br>
      post.author: {{ post.author }}<br>
    </li>
  {% endfor %}
</ul>

{% endraw %}

And this is the list that was generated:

{% for post in site.posts %}
• {{ post.title }}
  post.excerpt: {{ post.excerpt }}
  post.tags: {{ post.tags }}
  post.author: {{ post.author }}
  
{% endfor %}

Print list of tags:

{% raw %}

<ul>
  {% for post in site.posts %}
    <li>
      title: {{ post.title }}<br>tags: 
      {% for tag in post.tags %}
        {{ tag }},
      {% endfor %}
    </li>
  {% endfor %}
</ul>
</ul>

{% endraw %}

{% for post in site.posts %}
• title: {{ post.title }}
  tags: {% for tag in post.tags %} {{ tag }}, {% endfor %}
{% endfor %}