In my program, I need to generate dynamic number and dynamic size of textures.So I write a function to do this

I am trying to understand what OpenGL actually is and how it is written.
I do understand that it is used for graphics related rendering and manipluation of 2d or 3d graphics. What i don’t understand is people saying that OpenGL is an API and its not written in c or c++ but rather c/c++ calls this API to interact with OpenGL.
So does this mean OpenGL is written in something even lower like Assembly , I just don’t understand how it is created and how you would call it from other languages without calling the c implementations/wrappers.
Since its an API it should make sense to be able to directly call it from other languages ?

I am new here. I am a student at a university in Europe and as a part of my course is a task to create a small (I think) project in OpenGL.

Every bindless texture example I can find uses sampler2D but is it possible to use samplerCube/sampler2DArray/sampler3d as well?

Take this example, where a cube light has hardcoded vertices and indices:

I made a framebuffer and connected it to two color attachments.