Version

glGetString​(GL_VERSION​);

There are many versions of OpenGl and they add more as often as possible to confuse everyone. Below are the ones that matter for now. Read about features that have been removed in newer version by looking at the deprecation page.

OpenGL

How much each version is supported can be found at http://www.g-truc.net. Since OpenGL 3.3 the GLSL version number is the same as the OpenGL version.

OpenGL ES