yeager uses Smarty as its template engine, because it offers a very flexible and clean way of templating. Smarty can be seen as a bridge between your Templates and yeager. 
You might want to check out the list of available variables and the example section. If you are not familiar with Smarty's syntax you should have a look at the Smarty documentation.

Specifying content areas

Each time a Template gets uploaded yeager parses the file and checks for available content areas and navigations.
Each content area defined in a Template represents a container into which you can assign Content Blocks when managing Pages or E-Mailings. The content of the assigned Content Blocks is available in your Template through the variable $contentareas. 
You also need to specifiy which Entry Masks can be displayed in a specific content area.
Please use the following syntax in order to specify a content area in your Template:
  1. <!-- contentarea begin: CONTENTAREA_NAME -->
  2. <!-- contentarea accepts: ENTRYMASK_IDENTIFIER1, ENTRYMASK_IDENTIFIER2  -->
  3. <div class="content">
  4. </div>
  5. <!-- contentarea end: CONTENTAREA_NAME -->
It is possible to display content without having any content areas in a Template configured. By making use of Page Extensions you can assign custom variables (including your custom content) to Smarty.

Specifying navigations

You should also specify at least one navigation in your Templates to make them available for selection on the "Appearance" tab when managing Pages:
  1. <!-- navi: menu_main -->
  2. <!-- navi: menu_meta -->