After page is created you can give yourself extra control of your design by using sub templates. They allow designers to define several additional content layouts, like 2 column contents, or content wrapped under certain class elements and can be re-used when needed.
Sub Templates can be placed in any block area on the page. They use same <mwPageArea> tag to define additional drop areas. This lets designers build indefinite layout trees allowing for complex content layouts.
Example Sub-Template for two column layout:
<mwPageArea rel="leftColumn" info="Left Column"></mwPageArea>
<mwPageArea rel="rightColumn" info="Right Column"></mwPageArea>
The above can be added to any page block area to give you a two column layout.
Example of page in live edit with no sub-template added:
Notice that there is only the content area that was defined by the page template.
Example of page in live edit after adding sub-template:
Now after adding a sub-template you see that there are 2 areas where you can add content. This way you can keep modifying your layouts without having to create multiple page templates to fit your design.
FTP directory structure