I was asked to answer some questions from a middle school student doing a research project on video games.  Since I am interested in the topic generally, I should probably figure out how to answer these kinds of questions at an age-appropriate level.  My attempt:

Jose asks:

1. Do video games affect the human brain? Do video games affect the way of thinking? Do video games damage the thinking part of the brain?

Yes, video games can affect your brain, like anything else that you do a lot of.  However, these changes can sometimes be for the better.  There is recent evidence of improvements in “visuospatial attention” (how you see the world) following video game play.  There may also be changes for the worse, like increasing aggression, but these are not yet well understood.
2. Can video games improve people’s knowledge?  Can they help people’s grades get better in school? Or can the[y] get bad grades?

Video games probably won’t help you in school very much.  They can cause problems in schoolwork when kids play too many games and don’t keep up with homework and assignments.  If you are getting your homework done, playing games won’t hurt and may actually help a little bit.
3. Can video games make people lose time? With friends and family? Time outside?

If you spend too much time on games and do not make time for friends, family, proper exercise and sleep, then that will very likely cause problems.
4. Can video games make people sick? Gain weight? Headaches or a tumor?

Some people report dizziness and nausea (upset stomach) from games that give you first person perspective.  This is very likely related to the kind of motion sickness you can get when riding in a car.  In rare cases, some people may react badly to flashing lights/sounds in video games.  In general, games won’t make you sick.  If you eat in an unhealthy way when playing videogames, that can lead to weight gain and other health problems.

5. Can video games make people addicted to what their mainly about? How do they do this? Why do people get addicted?

Gaming addiction is not well understood.  Games aren’t addictive the way other things are (like cigarettes).  However, there are certainly some people who have problems like in (2) and (3) above.  They seem to play so much that it messes up a lot of other things in their life.  That looks a lot like being addicted.  It also can look like a lot of other problems that teenagers often run into — mood swings, depression, difficulty in relating to others.  I do not think it is well known whether games can cause those problems or whether kids having those kinds of problems for another reason sometimes like to play a lot of videogames.

Thank you very much for your help.

You are welcome, Jose.