You are alerted about new messages via both email and a small notification button at the top right of the main window. (That notification also appears on your Gmail window.)

However, communicating with people is not quite as straightforward as it at first sounds, possibly because Google+ has a limited number of members at this point. For now, most of the people you put into circles can't communicate with you directly on Google+. Instead, they'll just get an email, which diminishes the usefulness of Google+ considerably. Until Google+ enters more widespread distribution, it will remain more a testbed than a useful communications tool.

Circles are the core of Google+, but there's more to the service as well. Sparks brings together the best of Google and social networking -- it's a simple way to find and share content that interests you and might interest people in your circles. (I assume that it's named Sparks because it's designed to spark online conversations.)

You can share any content in Sparks with all your followers or with specific circles or individuals by clicking a Share button.