Add new comment

From this article and it's comments I get answers to all my questions and could make everything works as I need (entry level, nothing complicated)! Awesome! Thanks to all of you a lot!
But what about Sessions? Could you point me to the description or write some words about this part of the program.
I understand that it is a place where I could add some commands to a specific program/connection, but what commands and when they executes I did not understand. When I load previously saved config it duplicates some clients/ports.
What is it for and when I should use it? Maybe you have some useful examples? Write it please.