A layout page is devided in different areas (fragments).
The main fragment is the most significant part of a layout page. Every layout page has a main fragment, which cannot be deleted. If there are sub pages configured, the main fragment will die displayed as static area in a transparent layer over the sub pages. It can be used for control elements that should be available in each view of a sub page.
The page header will be display at the top of the layoaut page. It exsits on every page and cannot be deleted. By default it is diplayed with a blue color gradient.
The context slieder will be displayed for additional information at the left border of the screen. It will be slided in by pressing the menu button in the left upper corner or with a slied movement at the left border. This fragment is optional, so you have to add it to your layout page if you want to use it.
If there are sub pages defined on you layout page, you have the choice to add one context slider which will be in effect for all subpages or you can define a context slieder seperately for each subpage.
With subpages you can define define different areas witch will be displayed like the main fragment on the biggest part of the display. You can switch between the subpages with a slide movement on the screen. If you have configured sub pages for your layout page, the main fragment only has a minor relevance. It will be displayed in a static way above the page layer.