Display entries for each month
You could do this multiple ways.

One you could create a category with each month and an input for your entries and assign that month to each category.  Then it would be a matter of calling that categories relatedTo param using each Month Category ID.

{% set monthIds = craft.categories.group('months').ids() %}

{% for monthId in monthIds %}
    &lt;div&gt;
        {# group each months entries #}
        {% for item in craft.entries.section('sectionName').relatedTo({targetElement:monthId}) %}
            {# content for each entry. #}
        {% endfor %}
    &lt;/div&gt;
{% endfor %}


Two you could use your eventStart field.

{# 1 == January #}
{% set months  = ["Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"] %}
{% for month in 1..12 %}
    &lt;div&gt;
        {# group each months entries #}
        {% set idx = month - 1%}
        &lt;h3&gt;{{ months[idx] }}&lt;/h3&gt;
        {% for item in craft.entries.section('blog') if item.eventStart|date("n") == month %}
            {# content for each entry. #}
            &lt;h3&gt;{{item.title}}&lt;/h3&gt;
        {% endfor %}
    &lt;/div&gt;
{% endfor %}