Easy questions here! (Just started need help)

1:How do you make gravity??
2:How do you make so when your Charakter stands where un objeckt(person) and push for example "Space" the other charakter says somethings to me in a dialog?[/b]
2:How do you make so when your Charakter stands where un objeckt(person) and push for example "Space" the other charakter says somethings to me in a dialog?[/b]