Anytime you follow someone new, you assign that person to a circle (in other words, you "add" them, in the G+ vernacular). Think of circles as fancy groups for organizing and managing your social experience. By default, the system provides you with circles for friends, family, and acquaintances, as well as for people you're following but don't know personally. You can add more circles and customize all sorts of stuff about the way they work (more on that in a bit).
Click the circle you want from the list at the top of the screen and your stream will show updates only from the people who are in that circle.
Basically, circles allow you to focus on content from specific groups of people; just click the circle you want from the list at the top of the screen and your stream will show updates only from the people who are in that circle. You can also view content from everyone in your circles collectively by selecting "All" from that same list.
Google+ does a pretty good job at helping you find and discover people to follow. When you sign in for the first time, the system will walk you through some steps to locate folks you know and connect with other interesting users you might not yet be acquainted with.
When you sign in for the first time, the system will walk you through some steps to locate folks you know and connect with interesting users.
You can always expand your circles later, too: From the desktop website, just hover your mouse over the word "Home" on the left side of the screen to access the main navigation menu, then click the "People" option. There, you'll find lists of people you might have a connection with, along with strangers whose content might interest you: celebrities, regular folks who talk about topics you like and even lowly tech writers who share stories about getting started on Google+.
Organizing your circles
While you're in the "People" section of Google+, click the link at the top of the screen labeled "Your circles." That'll bring you to a graphical tool with which you can adjust your circles by dragging and dropping people into different groups; you can also create or delete circles as needed.
A graphical tool lets you adjust your circles by dragging and dropping people into different groups.
When you click on any circle, you'll also find an option to share it. That allows you to post the circle publicly in order to let others see the group you've created. You might share your "Tech News" circle, for instance, to give other people your own recommendations of interesting G+ users who talk about technology. Shared circles are a great way to find new people and help your followers do the same.
Circles are useful when it comes to viewing content, but their greatest value may be in helping you share it. Circles make it easy for you to control who sees what you post on Google+; after all, some things might be okay for anyone to view -- but other things might be best left to the eyes of your friends, co-workers, or a few specific contacts.