Please refer my previous article to learn more about how to build a dictionary in SharePoint Designer 2013.
In this blog you will see how to use "Get an item from a Dictionary" action in SharePoint Designer 2013.
Get an Item from a Dictionary action is used to retrieve a variable stored in the Dictionary and placing it in a variable. This is valuable when you need a value in the dictionary stored in a stand-alone variable. You can retrieve a value by entering the name of the variable.
EmpName is the name of the variable in the Dictionary and it is being output to a new String variable named as Output .
Workflow Design:
Result: