Certain category and posts at the home/start page

https://codex.www.ads-software.com/Template_Tags/query_posts

That is great, but which file do I modify from the dashboard? Can someone walk me through it from the start?

I know that I paste this:
<?php
query_posts(‘cat=2’);
?>
before The Loop. For it to work on the home page, when someone first arrives at the site, what file do I change, and how do I get to that file?

Thanks!

Try editing your theme’s index.php file via Appearance -> Editor.

Thanks, esmi. That did the trick!!

I also could not find the category ID number, until I saw it in the URL. Where should I be looking to find Cat ID # and Page ID #?

See this Codex page.