The Main Screen is where you edit your page content. Select the page to edit by clicking on it from the Explorer Panel. You can easily format content, insert tables, hyperlinks, images, buttons, etc or the Right-click Menu (from right-clicking inside a page).
Down the right side of the main screen are some tabs (see left), called mode tabs. Not all the tabs will be visible, it depends on the page type you are editing.
Some templates contain one or more small EDIT buttons that allow you to insert extra content in the template area. This area is called Template Editable Area.
At the bottom of the main screen, there is status bar with some useful information. Starting from left to right it shows: current template, resolution, current page name [filename][page ID], page size in bytes. If the cursor is inside a table, you will also see current cell size.