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.
A good research question will lead to your thesis statement.
For example, the question...
what are the effects of violent video games on teenaged boys?
...might lead to the following thesis:
"Exposure to violent video games negatively affects teenagers in a variety of ways: It increases aggressive behavior, physiological arousal, aggressive-related thoughts and feelings, and also decreases prosocial behavior."
Strong thesis statements
or "why should I care?" test
Source: Thesis Statements. George Mason University.
Image source: Powernowllc. CC0 1.0. Wikimedia Commons.