If you have an account you can sign in by clicking on the "Sign in" at the bottom of any page.
When you are signed in, if you have edit privileges on this site you will see buttons at the top right of the page like this:
You can
--create another page in this site
--edit this page
--The "more actions" lets you edit site properties and settings.

When you create a page you will have the choice of type of pages like web page, or announcement, for example.

 Also notice when you are signed in on the Announcements page that you will see a new post button that will let you create a post which will be a new page that will also appear at the top of the Announcements page.


From more Actions you can do a bunch more including:

upload attachments like a Favicon, which is that little picture beside the site's name in the address bar or tab. 
Follow these instructions to Add a favicon

Under Site Appearance you can adjust the layout where you would add a logo to the header or you can change Colors and Fonts for the site.

Now to set the standard logo for the domain you have to go to the domain settings for Google Apps and under the Appearance tab you can upload an image to replace the Google logo on the web mail page, and user's calendar page for example.



*You can also use the Help link at the top right of the page when you are signed in for more information & instructions.