Session concept in Appian

Hi There is nothing like session here , but we use rule inputs, to be passed  among form fields and interfaces 

Rule Inputs and Parameterized Process Variables are used to pass data from one object to other.

We use rule inputs, to be passed CDT as well

You use rule inputs to pass data from one object to another object. Unlike OOPS, object aren't related to class here rather they mean the smallest division of an application. More like building blocks. 
Rule inputs are like parameters of a function which can accept values from outside of them,