b. Theme objects
“Regardless of how themes are built, a base understanding of CMS is needed. Standard CMS installations make use of four main elements in the layout. Left Blocks, Center Blocks, Right Blocks and Modules. You can create and modify the blocks via CMS's administration menus, but the theme controls when, where and how these four elements are displayed. Two additional elements are used for the news, the Summary Article (displayed on the Main Page) and the Full Article (displayed when the user reads the Full Article usually by clicking Read more...).” (Shawn McKenzie)
Let's look to these elements, that we call theme objects:

There are (from up to down in the picture above):
the Header: it's the upper stripe of MDPro that contains usually the site's logo, a banner, images, the language flags, the Welcome message, the top links or a drop down menu, date and time and other elements, that we will call commands, because “the locations where these objects are to be placed are specified in your HTML templates using comment commands, standard HTML comments that have an embedded AutoTheme command. AutoTheme commands are enclosed in brackets [ ] ” (Shawn McKenzie) and take the following form:
Example: <!-- [command] -->
<td><!-- [banner] --></td>
Left blocks: all the objects located usually on the left column of the site: usually because you will soon understand that with AT (AutoTheme) you're free to use or not all these locations or to place there every object you want, e.g. an image or nothing... Left blocks are usuallu the Main Menu and other blocks you place there from the Admin Panel >> Blocks configuration.
Center blocks: all the objects located usually under the header: normally the Messages from the omonym module. But you can place there other blocks: AT calls the free blocks location, that you can place freely where you want areablock1, areablock2, ....areablock9.
Right blocks: all the objects on the right column of the site: in the standard installation of MDPro you find there the Poll, Daily Archive module, etc.
Modules: it's the main central content of the page: per default, the News Module, but also the Statistic module, or Subjects or other types of site content. At's flexibility allows to show them with right blocks, and/or with central blocks, without any blocks only with header and footer, etc.
Footer: the footer is placed at the very bottom of the page: it's the standard Copyright notice that is set in the Admin Panel >> Settings >> Preferences. With the template you can also place here images, banners, everything you want...