Using the Google+ Sandbar in Other Google Products
The minute you start using Google+, you'll notice some new options in the upper-right corner of the bar that appears across the Google products you use. In Google+, you'll see your name, followed by a red square with a number in it, a Share button, and an icon with your picture in it. This bar at the top of all Google products has become known as the sandbar. This is where you'll be notified across any Google product that there are new updates (comments, new followers, shares) to your Google+ feed.
If you're a Gmail user or a Google Reader user, you'll notice that you can also use Google+ from those products as well, such that the Google+ experience follows you through every product you use on Google — and you don't even have to leave those products to use them! In any Google product, here is what you will find:
Your name: Clicking your name opens a pop-up window with options for going to your Google+ profile, jumping to your stream or your circles, adjusting personal and privacy settings, and logging out of Google.
The notification box: If you don't have any notifications, your box is gray with a gray zero in it, but as soon as you get new notifications, that square changes to red with a white number in it, showing the number of new notifications you have. Click this box, and you'll see notifications about all the new comments, shares, and new people circling you in your Google+ feed.
You can click the square even if it's gray to see old notifications.
The Share button: You can post to Google+ without even being in Google+! To do so, in any Google product with the sandbar installed, just click the Share button, and you're presented with a box to post to Google+.
Your profile picture: Clicking this picture gives you the same options as clicking your name.