You may have noticed that the familiar black menu bar at the top of your Gmail screen has disappeared. This change was recently made by Google and was pushed out to all accounts. The new interface may be familiar to individuals who use Android for Chrome OS. There is a small icon on the upper right of your account that expands to reveal a table of icons for the Google web apps.
Below is a graphical description of the differences and how to access the Web Apps from Google.
The Google bar runs across the top of many Google services and offers easy access to Google's products. It also helps you search, share, and manage your account.
The Google bar may contain a search box for the Google service you’re currently using. If you're a Google+ user, to the right you’ll also see a notifications icon and a Share button to share a post to Google+.
The Google bar’s notifications icon displays the number of unread Google+ notifications, which you can view by by clicking on the bell icon. You can also share to your circles on Google+ by clicking “Share” from the Google bar. The icons at the bottom of the box can be used to add photos, videos, links, or events to your post.
To sign out, switch accounts, or manage your account, click your picture on the upper right hand side and select the appropriate action. If you see your email address at the top instead of a photo, you can click that as well.
Even if you aren't signed in to your Google Account, you can still navigate to other Google products by clicking the App Launcher icon and selecting a specific product. Click "More" to reach additional options.
More information about these changes can be found at these Google blogs:
Edited 11/5/13 to remove the phrase "without advanced notice" from the second sentence in the first paragraph.