This diagram show how you could set up a bounce flash but there is different ideas as you can bounce light off a wall and the background, it doesn’t have to just be at the ceiling.
What is Bounce flash?
Bounce flash is were you don’t point the flash at the subject and you point it in the different direction to the subject to make the light less harsh on the subject. It increases light surface.
You do this to make the light less harsh and to stop the light for going flat.
Angle of incidence = Angle of reflectance
so if you had 35° it would come out again at 35°.