After the enabling the service, you need to wait a few minutes until you can use it. Obviously, users have to manually join Google+ by visiting plus.google.com. "Google Apps users will have access to the same set of features that are available to every Google+ user, and more. In addition to sharing publicly or with your circles, you'll also have the option to share with everyone in your organization, even if you haven't added all of those people to a circle," explains Google.
It's interesting that Google+ is available for higher education institutions, but not for other education institutions because users must be at least 18 years old to use Google+.
You probably noticed that Google+ evolves incredibly fast, faster than any other Google service. The support for Google Apps is not the only new feature: there's Hot on Google+ (a section that highlights popular posts), Ripples (a visualization tool for public shares and comments) and a Creative Kit for photo editing powered by Picnik.