If you're talking about putting content on your main page, that's done in Admin>Tools>Define Pages Editor. Select the page you want to edit from the dropdown.....example... (define_main_page.php).You can use either plain text or HTML, but in order to use the HTML Editor, you have to make sure it's turned on In Admin>Comfiguration>My Store..........Find HTML Editor (second from bottom) and select HTMLAREA.

Hope this helps.