i'm interrested in starting to learn abit about graphics programming through game development and i'm wondering what the pros/cons are when using Unity 3D over using something like C++ & openGL
asking Unity3D vs. C++ & OpenGL is like asking whether to buy a Car vs. or a Wheel. You either know how to build a car using it's parts or you need to use already built cars out there!
Unity 3D is an integrated development environment for game development. C++ and openGL are just tools you can use for game production.
It's hard to compare them because of that. For starters I'd suggest you finding a 2D game library for your favourite language and only then switching to c++ / openGL when you feel ready.