Dictionaries and word lists are a shortcut when you need to use many different words or sentences in the same way.
If you find yourself creating many rule with the same structure, you might be able to simplify your setup with a word lists or dictionaries.
This rule will move all files that contain the word "Coca-Cola" to the "Coca-Cola" folder.
But lets say you also need to do the same with "Pepsi", "Sprite" and "Fanta".
You could create three new rules, but it's much easier to create a "Soft Drink" word list and use this in a single rule.
Lets say you have files containing the names of customers, but want to organize the files into folders named by a customer number rather than the customer name.
This rule will use a dictionary to do this.
Dictionaries are similar to word lists, but allow you to specify another word or phrase that should be used in the action.