OpenGL Programming Guide, 6ed. It is current as of about 18 months ago.
If you are new to OpenGL, there is not much point in worrying about the latest & greatest features of v3.2... OpenGL builds on it's own concepts from version to version. You need to understand the basics of OpenGL before the very newest bits make any sense. While learning the basics you will find out what new parts are useful to you.
That said the org that manages OpenGL is called Khronos. This page has links to the standards docs and extensions: http://www.khronos.org/opengl/.
But really, learn the basics first: that and a bit of reading on the side will point you at what extensions or new features are worth your time.
[edit] As has been noted by other people in this thread: OpenGL is a C API.
There are C++ wrappers but in my experience they are more trouble than they are worth, they each impose a model of using OpenGL... but OpenGL is really just a collection of C functions and using it as such gives you the most flexibility.