In order to create a window you’ll need to interface with whatever windowing system is currently present on your operating system. This will either require system calls if the window manager runs in kernel space (as is the case in Windows) or some sort of interprocess communication for user space window managers (like X). To create the window from scratch, you’ll need to read up on how these window managers work and what protocols they use. In the case of X, it shouldn’t be too hard to find resources on how the protocol works. In the case of Windows, your only option might be to use the API, since the internals of the window manager are proprietary.