Rich, EE itself does the heavy lifting for your table joins. Most of the time you don’t need to do the heavy lifting yourself.
During the install process, there is a template group called site. In that template group you have a limited sample of tasks you can use with EE.
For instance, there is an example entry. The code is there to add a comment. There is a comments template, as well as an RSS feed, an archives page, referrers, trackbacks, etc.
In your example, you have a design with categories, ratings and comments.
Categories and comments are a part of the exp:weblog:entries tag. Ratings aren’t built into EE, but there is at least one third party offering.
If you look at the sample that comes with EE, you’ll see the following code:
<div id="blog">
{exp:weblog:category_heading weblog="{my_weblog}"}
<h2>{category_name}</h2>
<p>{if category_description}<br />
{category_description}<br />
{/if}<br />
{/exp:weblog:category_heading}</p>
<p><br />
{exp:weblog:entries weblog="{my_weblog}" orderby="date" sort="desc" limit="15" disable="member_data|trackbacks"}</p>
<p><div class="entry"></p>
<p>{date_heading}<br />
<h3 class="date">{entry_date format=' %l, %F %d, %Y '}</h3><br />
{/date_heading}</p>
<p><h2 class="title">{title}</h2><br />
{summary}</p>
<p>{body}</p>
<p>{extended}</p>
<p><div class="posted">Posted by {author} on {entry_date format='%m/%d'} at {entry_date format='%h:%i %A'}</p>
<p><br />
{categories}<br />
<a href="http://{path=site_index}">{category_name}</a> •<br />
{/categories}</p>
<p>{if allow_comments}<br />
({comment_total}) <a href="http://{url_title_path=">Comments</a> •<br />
{/if}</p>
<p>{if allow_trackbacks}<br />
({trackback_total}) <a href="http://{trackback_path=">Trackbacks</a> •<br />
{/if}<br />
<a href="http://{title_permalink={my_template_group}/index}">Permalink</a></p>
<p></div></p>
<p>{paginate}</p>
<p><div class="paginate"></p>
<p><span class="pagecount">Page {current_page} of {total_pages} pages</span> {pagination_links}</p>
<p></div></p>
<p>{/paginate}</p>
<p></div></p>
<p>{/exp:weblog:entries}</p>
<p></div>
{my_template_group} and {my_weblog} are assigned at the top of the template.
There are two tables that are used for weblogs or data containers.
exp_weblog_titles and exp_weblog_data.
Comments are found in exp_comments. You can join to it via the entry_id field, which is found in exp_weblog_titles and exp_weblog_data.
I have to run off to pick up grandchildren.. but is this of any help?