Question

A meta-analysis (Anderson & Bushman, 2001)

Answer 1

The correlation is 19 percent. That means there is a significant dependency of aggressive behaviour of the people on the time spent on playing video games.

It means that the more one spends time on playing video games, the more aggressive one becomes.  In other words people playing video games for significant duration develop aggressive behaviour.  Also, people who play less of video games are less aggressive.

19% of persons are aggressive because they spend a lot of time playing video games. 

19 % of Less aggressive persons are found spend less time on playing video games.

We can say that these relations are true to a confidence level, as there have been a lot of (21) controlled experiments to support this fact.