Professor Brain was experimenting to create waves that increase the brain power, like it can make you really smart, but his experiments went horribly wrong (as always) and made every person that came in contact with the waves DUMB.
Now they don't even know what to do and how to survive in their daily lives. In this disastrous situation professor got an idea to make an app where people can post their questions and get replies for their problems. Don't look surprised there is an app for literally anything these days. So he quickly makes an app and puts YOU in charge to answer all the questions.
Your job is to reply people the best you can in order to keep the balance of this planet. Just be cautious
Don't populate the earth too much
Don't make the humans go extinct
Don't make them too sad
Don't make them too happy
See how simple this was. Now go on help those poor souls and don't forget to have fun!