The value token
To place a saved value into text, use a token in the form {$scope:key}, for example {$workflow_var:order_id}. The Message step shows the hint "Insert a saved value with this token" right below the field.
Where values come from
A value is available once an earlier step saved it in the same run. That can be a Collect answer, the label of a tapped Options button, a field the AI collected, or a value returned by a Call API step. Nothing is filled in before the flow runs.
Where you can use it
Tokens work in message text, question prompts, the ending message, and Branch conditions. So the same collected value can be shown back to the customer and used to decide which path the flow takes.
If a value is missing
An unset token becomes empty text, not an error and not the literal token, so "Hi {$workflow_var:name}!" with no name reads "Hi !". If a value must always be present, add a Branch step that checks it is set before you use it.