how we make difference between output and input in data. pls explain me with example code

You should look into taking the various learning offerings at Appian Academy - many (if not all) primary questions like these will be answered upon completion of the learning exercises.  And you will also likely come out of it with the vocabulary necessary to put any remaining questions into terminology we can make sense.

Hi there,

It is pretty straightforward. Whenever you want to pass data inside a node or subprocess, then you use the input property of those. When you want to bring out the data from a node or a sub-process in the parent process' PV, then you use the output property. 

Additionally, you can make them null one by one and see the impact of it on your flow to understand it more in detail.