The way you used to log into Google+ (or the way I did, anyway) was by looking for the little "+Google" in the upper right corner of Google's homepage. Or when I was already logged in, I looked for "+Mark".
In an effort to "simplify the user interface," those +Names are now gone. You can still get to Google+, you just have to wind your way through a couple menus. Here's a little more info: Google+ profile links have started disappearing from Google | The Verge