NB: this functionality is currently under test.
You can receive notifications of changes to pages by "watching" them; just use the "watch" button towards the top right of a page. Pages that are already watched have an "unwatch" button instead. You need to log in to be able to watch pages.
A list of the pages you are watching is accessible as "My watchlist" under "personal tools".
To monitor changes you need to use a feed reader capable of