WIN32K.SYS is a low level component of WIndows. It’s the kernel side of the Windows subsystems. The includes the graphical user interface infrastructure including the USER, GDI and DirectX. DirectX is handled by DXH.SYS.
USER32.DLL and IMM32.DLL make up the window manager. GDI32.DLL MSIMG32.DLL make up GDI. D3D8THK.DLL is the DirectX thunk. TWSRC_32.DLL is the print driver. WINSRV.DLL is the console and hard error.
For device driver developers GENSRV.EXE generate USRSTUPS.C which can be compiled to make WIN32UMODE.LIB which can then be linked to a driver DLL.
At this level functions include memory management and handling shutdown. Threads are also managed with the kernel.
Callbacks are used to return results from a system call. A function makes a call, with a pointer to a handler that is called when the result is returned.
Low level calls here can be made to identify a video card or other installed device. Then an application (game) can proceed with known capacity.
Errors here are where BSOD crashes occur. This is because there are no high level functions to cope with errors. Low level components expect developers to be more competent.
If any of these file are identified with a crash, you will have to reinstall Windows as these are system components that should never be touched.