Write CUDA kernel

Hello:
I am following this tutorial,
http://numba.pydata.org/numba-doc/dev/cuda/kernels.html

the example is not so clear, anyone can give me a clue?

Cuz I dont code with C, but CUDA is based on C, and I want to use python, so sometimes its not so clear for me:)

Any advice will be appreciated, I have been stucked for days:)

Hao