From NEPA Crossroads Knowledge Base
The tabs on the top are grouped into three separate sections. The first group all the way to the left will indicate what type of page you are viewing. Typically for a standard article page there will be the "Page" tab and the "Discussion" tab. Whatever one you are viewing will be highlighted.
These are two distinct pages. The "Page" tab will contain the article itself. The "discussion" page is in sense the backroom of a page and can be used for discussion of an article. For example if you have a disagreement over what should be contained in an article with another member it can be discussed here.
The second group of tabs are indications as to what can be done with that page and are relative to whatever one is highlighted to the left. For example if you are viewing the "Page" and click the edit tab you'll be taken to the edit panel for editing the article. The page tab to the left will remain highlighted and the "Edit" tab will also now be highlighted. If you were viewing the "Discussion" and clicked the edit tab you'll be taken to the edit panel to edit the discussion. Be sure understand the differences between the two.
The last tab all the way to the right is for "Watching" or "Unwatching" an article. You can use this tab to monitor articles for changes. When you are watching an article it will be added to your "Watachlist" which can be accessed from the main links. This is essentially a favorites menu. You can also set in your preferences the option to receive an email notification in the event the article is modified by someone else.