The proof of the pudding is in the eating, so have a look at a demonstration web site here.

You can then add your own content from the site administrator here. You will need to use the Username "admin" and the Password "demo" (don't type the quotes). There are 1001 ways you can use a CMS, but if you want a simple demonstration, why not try to add a new page.

Log in and click on Static Content Manager icon.
In the window that opens, click on the icon New (an icon on the line below the menu).
In the window that opens, add a title and some text. Then press save.
You will see your new page in the list. Click on the title and when the page opens again you will see a "tab" on the right hand side that says "Link to Menu".
Click on this, then click on "main menu" (where it says "Select a Menu"). Then write something in box by "Menu Item Name". Your page will appear on the main menu as this.
Click on the "Link to Menu" button.
Select the menu item Site -> Preview -> In new window - and go and visit your page in the browser window that opens.

See the Mambo web site here