O, rly? I learned OpenGL 4.3 entirely from specification.

Lucky you! :)

Although it is totally impossible for someone who don't have a prior knowledge about the matter.

Specification, as its name implies, is not a programmers guide. It just specifies functions and parameters.

I'm writing a tutorial series aimed at beginners wanting to learn the programmable pipeline and GLSL shaders, check it out here:

https://github.com/mattdesl/lwjgl-basics/wiki