Callouts pull something out of the flow of a page: a worked example, a definition, a warning.
Adding one
Click into the page where you want it, type /, and pick from the menu. Typing after the slash filters the list.
Scroll to Callouts and pick one of the five presets.
Example for a worked example.
Key term for a definition students should remember.
Tip for advice.
Warning for a common mistake.
Note for an aside.
They differ only in styling, so pick the one whose look matches the job. For a neutral box, use Note and restyle it.