How to use reference process?

Hi, my query is very simple all i need to know is how we can use that “reference process” .
here is what i have done so far but i am not successfulll… :frowning:

Parent process :

Receive step – > My info task – > Refernce process(child process) – > Modified Info Task-- > End

Child Process :

Receive Step (for syncronous reply) – > Modify Incoming Data Task – > Reply Step.

IN parent process i have set properties for “Refernce process(child process)” .and i have provided the start / Return documents but stilll it is not working i have given the same document which “Receive Step (for syncronous reply)” expects in “start / Return documents input document” but i dont know its not working!

Welll so any of you if ever have used reference process please let me know. Thanks in advance.