If you're a complete beginner in data parallel programming, and you're having trouble finding good intro material for OpenCL, it might almost be worthwhile to check out CUDA instead. In terms of the programming model, OpenCL and CUDA are identical - significant differences don't come about until you start optimizing for specific devices.

I learned CUDA first on my own, and then took an OpenCL class and found that the whole first section was completely redundant. There's also a pretty great wealth of CUDA material online and a few published books if that's your sort of thing.