<%Page path="/bits/header"%> Please go to 'Content Editor' and create a new content element named 'about_us'. Once you do that you should be able to see that element content below and on a separate page. You can then experiment with preview mode, reverting and publishing.
Content Editor
This is a set of templates that should be copied to the admin area of the real site (probably with some minor modifications).

'about_us' content
Separate page with "about_us" content.

'about_us' visible as source just to show more ways to use it:
<%Content/h name="about_us" default.path="/bits/about-us"%>

A couple of more content pieces to make editing more interesting:
Source of index page:
<%Page/h path="/index.html" unparsed%>
<%Page path="/bits/footer"%>