You can have as many circles as you wish, creating new ones by clicking on the circles icon.

When you create a circle, no one but you can see what you’ve called that circle, nor can they see those you choose to add into it unless you enable it from within your privacy settings. Otherwise, all that anyone can see is that you added them into a circle, not what that circle is called.
This makes it easy for you to organize your contacts, so that you are able to identify groups of people based on your circle names.

Begin by creating a few different circles based on the groups of people that you plan to communicate with. You can easily find existing Google+ contacts by entering in part of their name or email address into the search box at the top of your Google account’s main page, as shown below:

If the person or business you are searching for is already on Google+, they will appear within the search results window otherwise you will be given the option to invite them to Google+.
Google will also suggest users based on your existing gmail contacts, and these users will appear along the top of your Google+ circle page:
When you see someone that you’d like to add to your circle, drag their name into an existing circle, or to create a new circle, drag them into the blank circle that is visible on your profile page.