Most resources available online are very outdated. Specifically, they are all about OpenGL 2 which matches to DirectX 9.
The current specification is 3.2 which is equivalent (or, well, very close) to DirectX 10 (11). But the specification itself is very hard to read. In contrast, DirectX SDK is a wonderful piece of documentation, samples, and tools.
Where I can get the programming guide for OpenGL, that is not outdated? Where can I get the samples? And so on.
The OpenGL Technical Wiki is a starting point. It also contains some OpenGL 3.2 tutorials. Don't expect anything like the DirectX SDK, but afaik there's no better resource. OpenGL learning seems to be more like a trial and error process, where the developer forum is especially helpful.
Well, if you have no real experience of OpenGL, stick to OpenGL 2.0. If you want go to 3.2, I recommand reading the specs:
http://www.opengl.org/registry/doc/glspec32.core.20090803.pdf
and gl-extensions:
About samples, you can check humus website, it's really up to date and there's plenty of GL/DX materials:
