Bookmarks let you easily keep track of pages you think are interesting.
You have no Bookmarks. To add a page click "Bookmark this page" at the bottom of the page.
Bolded items have been modified since you last viewed them. Clicking diff will show you the differences between the version of the page you last saw and the current version, or will show the most recent difference (if only one change has been made since you last viewed the page).