How To Make a Full-Content Page With This Theme

where are you stuck?

– making a page template?

— see http://codex.wordpress.org/Pages#Page_Templates
— possibly start with a copy of page.php, then remove the get_sidebar() code;

– adjusting the content width to stretch to the full space?

— use a tool such as Firebug http://getfirebug.com/ to identify the involved styles
— check a css tutorial http://www.w3schools.com/css/

at any time, feel free to post a link to your site to demonstrate what you have so far.

looking at the site linked to your username:

you seem to have created a page template fullwidth.php and removed the sidebar from it;

to stretch the content, possibly add this to the end of style.css:

.page-template-fullwidth-php .blog_boxes{width:100%;}