Using this feature is as easy as subscribing to a normal RSS feed – simply enter the URL of the site in the Add Subscription box and hit enter. For a feed-less site, Google Reader will automatically show you a dialog box with an option to Create a Feed.
GReader will setup a monitoring service for the page and intimate you of any changes when they occur.
Earlier on, the only options for monitoring a site for changes were third-party services like Page2RSS, Feed43 etc. – which acted as an intermediary layer between your feed reader and the site and provided you with RSS feeds from the target site’s content. To view the feeds, you were required to subscribe to the URL provided by these services using your feed reader.
With Google Reader, you’re essentially able to bypass this middle layer altogether – as both the conversion of a static site to RSS and the reading of RSS feeds will be handled by GReader itself.
If normal feeds are anything to go by, this service may very well double up as an archiving system for a particular web-page by keeping a detailed record of changes of time.