Where there used to be an Email link in the footer of each item you will now find Share. Clicking or pressing it slides open a menu that now contains a Google Reader option in addition to Email. Selecting Google Reader will add the entry to your shared items list and display a check. The check will persist until the page is reloaded and selecting Google Reader again will unshare the item.
If you haven't authorized Google Reader access yet an authorization window will pop-up the first time you click the link. Syncing does not need to be enabled for sharing items.