When Google Plus originally launched in late June 2011, people could only join by obtaining an invite by email. Google has since opened the social network to the public, so anyone can join for free. To sign up, all you need to do is visit plus.google.com and type in some basic information about yourself. After clicking "Join" Google Plus will suggest some from friends who are already on Google Plus to add to your network, or your "circles."
What are Circles on Google Plus?
Circles are one of the main elements of Google Plus for business. You can create as many circles as you want and organize them with labels. For example, you may have a circle for friends, another for family and another for colleagues.
When you come across new profiles on Google Plus, you can drag and drop them using your mouse into any circle of your choice.
Building profile on Google Plus for business