How Can I use OpenCL?

Accelerated Computing CUDA CUDA Programming and Performance
1

Hi Experts,

   I am new to GPU programming. Last week only i have learned how to add cuda kernels with my application.So, please someone could explain what is openCL? and how can i use this?
   I hope the answer would be useful for every one new to this field.... :)

Thanks in Advance,

Karguvel