The instructions are here: http://support.google.com/accounts/bin/answer.py?hl=en&answer=98083
Above I said that I had never seen a practical use for Google+. This is not strictly true. A few months ago I had circles and stuff, and would have been fine with it, but the Gmail page would always announce activity among those in my circles. It was distracting, and though some of what was going on was interesting, little of it related to anything that needed the sort of immediate attention Gmail seemed to suggest.