1. Privacy and Your Circles
Differences between Google+ circles and Twitter followers or Facebook friends
2. Control What People Know About You From Your ProfileTo edit your profile settings, click on the button that looks like a circle with a silhouette in it, then click the "Edit Profile" button.
Want to check what your profile looks like to someone else? There's a "View profile as..." input field at the top right of your profile where you can check.
Who's in your circles/Which circles you are in. While you're at it (editing your profile page), you can also change the visibility of the people in your social network. Look to the left column. Under your circles lists, click on the "Change who is visible here" to control who can see all the people you have in your circles (i.e., who you're following) as well as everyone who has you in their circles (who are following you).
Again, by default, everyone on the web can see who you've added to your circles and who has added you to theirs. This, however, is highly customizable.