If you shout really loudly here on Earth a lot of people will hear you. But did you know that if you were in space nobody would hear you, no matter how loudly you shouted?
So why is there no sound in space?
When you shout, your vocal cords vibrate producing sound waves. Here on Earth, the waves are transmitted through air molecules. When the waves reach an ear, someone hears you shout. Air is the medium in which sounds travel. We know sound always needs a medium to travel through.
As well as gases, sounds travel through liquids and solids. In space, there are no molecules in the large empty areas between stars and planets. We say space is a vacuum. With no molecules in the vacuum of space, there is no medium for the sound waves to travel through.
So there is no sound. And that is the reason nobody can hear you shout in space.