Once you have selected an initial topic, the next step is to develop research questions. You'll do this by using probing questions, such as what, why, when, how, would/could, should.
Phrasing your topic in the form of questions helps direct the research process.
WHAT questions focus on a particular aspect of the topic: What is the driving force behind the popularity of video games? 
WHY questions ask for an explanation of something--why something happened, why it did not happen, or why one thing is better than another. For instance, why are video games so popular among young teenage boys?
WHEN questions focus on timing or history. When did video games start to become popular? When were video games invented?
WHERE questions focus the topic on a location, either geographical or other. Where, or in which countries, are video games most popular?
HOW questions focus aspects of the topic, on a process, or on the origin. How do video games affect users?

WOULD / COULD questions focus on possibilities. Would video games be more popular with teenage girls if marketing targeted girls?
SHOULD questions focus on the appropriateness of a particular action, policy, procedure, or decision. Should the government regulate violent video games?
Source: Mike Palmquest. Bedford Researcher. Colorado State University.