In your zencart ADMIN CONSOLE, look under the TOOLS MENU and go to DEFINE PAGES EDITOR

Open the define_main_page.php for editing and add content to your heart's content...

There are numerous sidebox modules available that can carry additional content. The late (and great) Clyde Jones's TESTIMONIALS MANAGER is a good one... Google like this one.

You can build your own sideboxes using BLANK SIDEBOX and CLONES of it, to contain reams of content if you wish...

There are scores of ways of adding good, relevant and topical content to your site, and the home page is no exception....