A page includes several editable regions. Editable regions are locations on the page where you can add or edit content. The editable region buttons are shown as green buttons on the page after you have clicked the Edit button in the Page Actions Toolbar.
The following image shows all the editable regions of a page, each is edited separately from the other regions. All regions are optional. The Intro Content region is formatted to be full screen width with a grey background and a partial gold bottom border at the top of the page. The Main Content region is the center area of the screen-width and the Additional Content region allows you to create full screen-width content.
When turned on in Properties > Parameters, pages will also have two additional regions—Left Sidebar Content and Right Sidebar Content. Left Sidebar Content is the area beneath the left navigation and Right Sidebar Content is the right sidebar.
Clicking a green Editable Region button allows you to edit that area using the TinyMCE content editor.