There are three main areas (labeled 1, 2 & 3 above):

1. The left-hand menu allows you to switch between various TYPO3 modules. As shown, the "Page" module is in use. This is the most common module to use when editing pages. (Note that the precise list of modules available may differ between users).
2. The second column shows the "page tree" (as it always does when the page module is in use). This shows all the pages available on the website - or at any rate the pages in the part of the website you are entitled to edit. The pages are organised in a tree - rather like the files and folders on a PC). Currently the page entitled "Exercise 1" is selected. The full path to this page can be read from the tree. It is:
   
   Help ›› TYPO3 ›› Editing Existing Content
   
   This path will be shown in the "breadcrumb trail" when the page is viewed.
3. The third column shows the editing panel - see below.

The editing panel

The panel has three column labeled "LEFT", "NORMAL" and "RIGHT". The CS website uses these columns as follows:

LEFT

This is used for adding custom menu items to the left-hand column of a web page. Frequently this will be left blank in which case the left-hand column will just show the automatically generated menu. (see Automatic Menus)

NORMAL

This is where the main page content is placed. See below for how to add and edit content.

RIGHT

CS pages do not have a right-hand column so in the great majority of cases this column can be ignored. (It is used for a few pages which have specialised layout requirements but this can be ignored for now).