Earlier quoted context omitted.
IIRC WinG was basically a way to set up a GDI device context that corresponded to a frame buffer, so you could take your DOS SuperVGA code and run it under Windows, only redoing sound and input. It's been almost 30 years though. :)
That's what it was, mostly. You could do pretty decent games using GDI as long as you just wanted to blit some sprites and were very much adhering to what GDI would give you. If I remember correctly, all the examples in the "GameSDK sampler CD-ROM" (the original name of DirectX 1.0) were in fact not done with GameSDK or even with WinG, but straight GDI.
Don't ask me how you do that, though it probably would not take me too much to page that stuff back into my brain by looking at the Microsoft Win32 manuals. Maybe CreateDIBSection? I still remember my kernel32.dll, but not GDI or User.
Anyway, what WinG did (and all it did) was speeding up the blitting part.