I'm having trouble realizing the difference between OpenGL and programs such as Unity, Maya etc. and how they are implemented. I have seen Unity export to Xcode but I don't see the role OpenGL has with them. Can someone please explain what the differences between them are? And Do I individually study OpenGL or should I study one of the programs like Unity? I have searched the internet and I am still confused with this. Its important for me to find out and understand this so that I can get the right tutorial/book which I will spend lots of time learning.