The Wh words are also called the Journalist's Questions in many style guides as well as introductory Journalism. Basically, whenever a Journalist is assigned a task of reporting an event (such as a presidential campaign or release of a product) that he/she has no knowledge of, the first starting point of investigation (or brainstorming) to create a story are the Journalist's Questions.
For example, in case of a presidential campaign:
- Who are the candidates? What's their background?
- What are they all campaigning about?
- When is the campaign going to start?
- Where exactly (states or counties) is the campaign going to take place?
- How (what process, expenses, business contacts, etc.) is the campaign going to happen?
So, to answer your question, the Wh questions are to be used when you want to investigate or brainstorm about an unknown topic.