3.3 and 3.2 don’t make much of a difference.
I think what people (at least used to) call “modern OpenGL” started with 3.0, and since 3.2 it has a “core profile” that enforces using only the new (GL3+) way of doing things and not the older deprecated stuff.
this one seems to be for SDL1.2, so it’s probably not too useful, also the code there doesn’t really look like modern GL
BTW, I found the tutorials at https://open.gl/ helpful.
Also, once you’ve got an OpenGL window (with a simple triangle in it) working with SDL, you should be able to follow any GL3 tutorials - all the OpenGL rendering stuff is the same, no matter if you’re using SDL or SFML or whatever. Just window- and context-creation (and OpenGL function pointer loading) is a bit different.
I think I also used http://www.opengl-tutorial.org/ as an additional resource for learning, it’s sometimes helpful to have the same things explained by different people to finally understand it oneself.