What: Turning the abstract (sad, afraid) into something sensed or behaved that the reader infers.
Why: The reader believes what they see and feel, not what is dictated; showing involves them, telling excludes them.
How: Instead of naming the feeling, write its effect: a trembling hand, an escaping glance, a breaking voice.
Common mistake: 'He was very angry' instead of an action that reveals the anger.
Exercise: Rewrite a sentence that names a feeling so it shows it through behaviour or a sensory detail.