To tell someone to be quiet by saying 'shush'.
Shushing is usually done when someone is being too loud or when you want to listen to something important.
Examples:
Shush, the baby is sleeping.
I had to shush the dog because it was barking too much.
Shush! I'm trying to hear the birds sing.
Shush, the cat is trying to sleep.
Shush! The aliens might hear us.
She shushed the noisy children at the library.