How do you view the HTML files? To know the Div's you are customizing?
View the source code in your browser, or install the Firebug add-on in Firefox, or use the Web Inspector in Safari or Chrome, or the one built into Explorer 8 and 9.
How do you change background colors?
Find the appropriate ID or class for the element you want to change the background color on and edit the color code. Many themes here allow the main background to be customized right from within the dashboard either with an image or color.
How do you change layouts?
Some themes have multiple layouts build in and some do not. If the theme has multiple layouts, they would be under theme options. In some themes you can hide or change page elements on a page-by-page basis in the CSS and in some you cannot.
Do note that CSS is a styling document used by browser to format, style and position the various elements of a webpage. It cannot be used to add or change functionality.
There are the forums for help, and you can contact wordpress.COM support using the contact form at http://en.support.wordpress.com/contact/ . They don't do phone support.