Question

I am learning OpenGL from this tutorial.
My question is about the specification in general, not about a specific function or topic.
When seeing code like the following:

glGenBuffers(1, &positionBufferObject);
glBindBuffer(GL_ARRAY_BUFFER, positionBufferObject);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertexPositions), vertexPositions, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);

I’m confused about the utility of calling the bind functions before and after setting the buffer data.
It seems superfluous to me, due to my inexperience with OpenGL and Computer Graphics in general.

The man page says that:

glBindBuffer lets you create or use a named buffer object. Calling glBindBuffer with target set to
GL_ARRAY_BUFFER, GL_ELEMENT_ARRAY_BUFFER, GL_PIXEL_PACK_BUFFER or GL_PIXEL_UNPACK_BUFFER and buffer set to the
name of the new buffer object binds the buffer object name to the target. When a buffer object is bound to a
target, the previous binding for that target is automatically broken.

What exactly is the concept/utility of ‘binding’ something to a ‘target’ ?

Answer 1

the commands in opengl don’t exist in isolation. they assume the existence of a context. one way to think of this is that there is, hidden in the background, an opengl object, and the functions are methods on that object.

so when you call a function, what it does depends on the arguments, of course, but also on the internal state of opengl – on the context/object.

this is very clear with bind, which says “set this as the current X”. then later functions modify the “current X” (where X might be buffer, for example). [update:] and as you say, the thing that is being set (the attribute in the object, or the “data member”) is the first argument to bind. so GL_ARRAY_BUFFER names a particular thing that you are setting.

and to answer the second part of the question – setting it to 0 simply clears the value so you don’t accidentally make unplanned changes elsewhere.