Might have code. Don't know what to do with it. To put categories on pages

Have searched for a few days. Must try asking for help here.

Seems like all the plugins I could have possibly used (for getting categorized posts to display on pages with an excerpt) do not work with 3.1.

I know how to find my php files and open them in a text editor.

Again, what I need to do is make the titles of posts AND an excerpt of it appear on pages. Not on the sidebar. Another way of saying that is posts will be categorized before they’re published, and pages need to display their corresponding categories’ content.

I think some code like this will do that:

<?php
query_posts(‘category_name=HOME&showposts=12’);
while (have_posts()) :
the_post();
?>

BUT
1) code like that will not display excerpts (before <–more–>) and I don’t know what code would,
2) I don’t know what php file to put code so each of the pages I create can display different categorized content
3) I don’t know where to put code so the default home page (which doesn’t appear in my Pages list) displays categorized content
4) If I did find out which php files to work with for this, I wouldn’t know where in these php files it should go
5) I think I need to create a single template for this, and am thinking there might be
a. a template of some kind somewhere with which to make a template like this so I don’t have to attempt to start from scratch, and
b. a note about what to name it for a page that lists categorized posts, and
c. a note about exactly where to put this file.

I know this is ridiculously elementary, but I can’t think of anything else to do, and I’m down to about $.50 an hour for the price I agreed to build this site for!