where all can the cuda be aaplied?

i m new to CUDA programming.so i sometimes dont know where to use CUDA as there are places where CPU takes less time to execute a loop than GPU.How to identify where to use the CUDA functions?

As a fast reply, I would write : every time you could parallelize a processus without interlocking or too much communication between threads.

The real answer may be much more complicated, with many if or when … :-)