cascading prompts are prompts where the values displayed in prompt two, are dependend on the value entered in prompt one.
ie: the first prompt shows country, the second prompt shows only the values for the choosen country.
You are talking about using a prompt value in multiple WHERE clauses. Since you’re asking it in Reporter, you will have to create the first prompt and select ‘show list of prompts’ for any following clause. Since you’re asking about previous (2) month, you will have to create a construction in which you substract one/two months from the input given in the prompt.
Cascading prompts work the other way as explained by highandstoned. In your case, you can create a prompt object in the universe that prompts for the current month. At the same time, you can create 1 or 2 more objects that subtracts first and second months using a function similar to AddMonths in Oracle and then drag the date object to compare with the created objects in the conditions pane something like