Looking to use a tag slug/URI and loop through entries of that tag
Here's a really DRY way to do it.

Setup a route, something like "news/tags/(tag)" to load the "news/index" template (the same one used for listing all entries).

In the "news/index" template:

{# If there is a tag token in the URL, set a filtered variable. #}
{% if tag is defined %}

    &lt;h2&gt;Tag: {{ tag }}&lt;/h2&gt;

    {% set tag = craft.tags.name(tag).first() %}

    {% set entriesToShow = craft.entries.section('news').relatedTo(tag) %}

{% else %} {# No tag token in URL, assume unfiltered overview page. #}

    {% set entriesToShow = craft.entries.section('news') %}

{% endif %}

{# the entry loop for both filtered and unfiltered entries #}
{% for entry in entriesToShow %} 
    {# display entry #}
{% endfor %}


When templating tag links to this system use:

{{ siteUrl }}news/tag/{{ tag.name|url_encode }}


This method allows you to reuse your entry loop and you don't even need a "tags" template. I can also be expanded to filter by categories as well without needing another template.