How to show a preview of a post? (Using Jekyll Bootstrap theme)

This also works at least as of 1.0.0, is built in and is simple to use.

<ul>
  {% for post in site.posts %}
    <li>
      <a href="https://stackoverflow.com/questions/10859175/{{ post.url }}">{{ post.title }}</a>
      <p>{{ post.excerpt }}</p>
    </li>
  {% endfor %}
</ul>

See here.