How to take value submitted from one interface to another interface

Have you gone through the developer course?
academy.appian.com/

There are 2 main ways of doing it. 

1. Call an interface inside another one pass the value from parent to child. 
2. Call  both the interface in a process model (as User input tasks) and facilitate the transfer of data from RI to AC to PV to next node's AC and then back to the next node's RI. 

RI - Rule Input
AC - Activity Class Input/Node Input
PV - Process variable

www.youtube.com/watch