Hi Jesus, "Don't all shout out at once! One at a time please!" should be "Everybody, don't shout all at once! One at a time please!" or "Please stop yelling at the same time! One at a time please!" Shout out is more often used like this by natives: "I would like to give a shout out to my family" or simply "A shout to my family" Which means you're saying hello/hi to your family or that you're sending a message to your family. Hope this helps!

It's expression that is saying "Don't speak all at once" or "Don't talk all at once." American tend to exaggerate a lot so we say "Don't shout out all at once" instead of saying "Don't talk or speak all at once."

can you understand it in chinese?if you can ,maybe I can help you