Welcome to this barebone OpenGL project !
It is meant for you to copy-paste and use as a starting point for your own projects.
(NB : if you are not planning on learning how to make a computer graphics application from scratch, you should consider using a more fully-featured framework like Cool).
You need to install CMake.
To use CMake I recommend this VS Code extension : ms-vscode.cmake-tools. You will need to setup the extension with a compiler. Here is the tutorial. It is based on Linux but at the bottom of the page you will find the explanations to adapt it for Windows and Mac.
Alternatively you can just create a build folder at the root of this project, open a terminal and run cmake .. ; chances are it will detect what compiler you have installed and generate the appropriate Makefile / Visual Studio solution / Xcode project.
In here we initialize glfw (the library that handles the window and user inputs), create a window and then start the app. You don't really need to modify this file, except to change your window name or initial size.
This is the actual root of your project. This is where your drawing code should go, as well as handling inputs from the user.
To learn more about the parameters you receive in the callbacks, read glfw's documentation.
The assets folder will be copied to the folder where your executable is created. You can put all the assets that your project needs in there, like textures, shaders, 3D models etc.