Your watchlist is a display for tracking changes, and is limited to showing changes only across your set of "watched" pages. You can see your watchlist by following the "Watchlist for notifications" link after clicking the person icon (on the top right). This feature is only available to users who have registered and logged in.
Before you see anything interesting here, you have to actually add some pages to your watchlist. Do so by navigating to a page that interests you, and click Actions > Watch.
Typically you would watch pages related to your interest areas, and also pages where you care most about the content. If you make a significant edit to a page, you might want to watch the page (so you know when there are any follow-up edits). Note that there is a also a checkbox on the edit screen ("Watch this page") for this purpose.
On the watchlist display, some page names appear in bold. This indicates whether or not you have visited the page to see the change. It's a bit like read/unread emails in an email inbox.
According to the relevant preferences, changes to pages you watch may also be notified to you by email. The main preference for this is "Email me when a page or a file on my watchlist is changed".
After receiving an email notification for a page, you have to visit the page while logged in if you want to be notified of further changes to the same page.