Hello,
The following are the only good free resources that I am aware of:
FreeVGA
OSDev Wiki
In addition, there are books that cover VGA in depth. Please note the VGAs limitations; OpenGL is typically used with SVGA+ resolutions which VGA does not support. VGA is limited to 640x480x16 color; anything higher requires SVGA+ modes.
In alternative solution is using the VBE or the Video BIOS; both will require v86 mode.