So, the trick is that sound needs something to travel through to reach your ears so you can hear it. When you talk, you make vibrations in the air, and those vibrations will move through the air and hit someone else's ears, and they can hear it.

It doesn't need to be air, sound can travel through things like walls or water, just not the same way as it would through the air.

But space doesn't have enough of anything between planets and stars and asteroids for sound to work. The vibrations can't go anywhere, they need something to travel through.

So, in order to make sound work in space, you would need to fill up all the space between stars and planets and asteroids with something. Like air or water, something that sound can move through.

How sound would work now would depend on what you chose, but also this is such a gigantic change to space that it's hard to figure out what would happen next.