Hi,
xooArticles Publishing Software uses
Smarty as a template engine. You can check their manual to understand how it works.
Script templates are located in a special directory in the script called 'templates'. There you can see a template directory now called 'Default' as now xooArticles script has only one default template.
There are tpl files inside this directory and if you want to change your site look and feel you should modify these templates. They are simple HTML files but they have some smarty tags and constructions like {if}, {foreach} etc.
So you can create a test layout and I will advise you how to modify it to fit our articles script. Feel free to ask questions in case you have them.