Condensed from Wikipedia -
Google+ (pronounced and sometimes written as Google Plus) is a social networking that also associates web-content like Gmail, +1 button, and YouTube comments directly with its owner/author. It is the second-largest social networking site in the world after Facebook. In October 2013, Google counted 540 million active users who used at least one Google+ service, of which 300 million users are active in "the stream."
A Google+ User profile includes basic social networking elements like a profile photo, about section, background photo, previous work and school history, interests, places lived and an area to post status updates. It also includes several identity service sections, such as a contributor and other profiles area that let one link their "properties across the web," other social media accounts one has, any blogs one owns or have written or sites one is a contributor to.
Circles enable users to organize people into groups or lists for sharing specific private content to only that circle, Work themed content can be shared with only work colleagues, family could sees more personal content and photos for example. The option to share Public or with Everyone is always available. A user may click on a Circle on the left side of the page, so his or her stream or news feed will contain only posts shared by users in that Circle.
Hangouts are free video conferencing calls with up to 10 people, done through the Google+ website or mobile app. Many apps can be used inside the hangout, allowing users to share documents, a scratchpad or their screens with other users such as YouTube, Google Docs, and Capture.