Stay away from NeHe tutorials, they are badly written and really old. Pretty much everything they cover is deprecated and done in otherwise old fashioned ways.

This is a big problem with OpenGL tutorials in general, a lot of them cover old stuff that shouldn't be used any more.

The entire OpenGL fixed function pipeline is deprecated, replaced by programmable shader pipeline. It's a lot more work to get simple stuff done with shaders but it pays off in the end.

If you're looking to write a game (and not an engine) it may be a good idea to get an engine and not write "raw" OpenGL at all.

If all you're looking to do is simple stuff (like get a rectangle on the screen), shaders are not required, correct?

You do need shaders for pretty much everything.

But if you only want to draw a rectangle with a solid color, you can do that using the scissor test and clearing "the screen". But that's about all you can do without shaders.

They are, unless you use old deprecated versions of OpenGL.

So the simplest program using the simplest shader would use a pass-through shader that doesn't modify the inputs?

My understanding is that the NeHe tutorials are archaic and do not properly reflect modern OpenGL usage. Iirc the legacy constructs used in NeHe have been dropped in mobile implementations of OGL.