The Ask search allows a user to configure and save a search with attributes which are pre-defined (constant) and also have some attributes which need to be updated on run time (dynamic).
Example: Assume you need to run a search every day with same publication, section, asset type attributes already defined and you just need to update the "created on" attribute everyday. So, instead of creating a new search everyday, you can create and save the search with the "created on" attribute defined as an ask condition.
So, next time you run this saved search, it will ask you enter the date for the "created on" attribute and you won't have to enter the values for the other attributes (Pub, Sec, Asset type etc) since they have been already defined and are constant
Hope this information is helpful.