Image 1 is the first thing a user will see when they start up a ChromeOS machine for the first time.
Image 2 is the new login screen for ChromeOS that will be used to select which user to login as. After logging in I believe you'll be restored with all of your tabs/extensions/bookmarks just where you were when you left off on any other ChromeOS device.
Image 3 is one of the ways ChromeOS will support switching tabs (possibly windows too, I'm unsure).
Credit for the 3rd image goes to the GoogleOperatingSystem blog which is definitely worth taking a look at!