Shout it Out is found in the Lesson Activity Builder, which you can access if you click the icon of the blue magic hat in the toolbar.
You can use it to allow students to share opinions, state preferences, add substantiating evidence etc. New in 15.2, you can move student ideas from one category to another. What I like about Shout it Out, is that it can be used so easily on the fly and it is part of a suite that is already powerful.
If you are not sure how to use it, see the tutorial found in Help in the top menu of Notebook.