What does “show, don't tell” mean?

“Show, don't tell” is the advice to let the reader experience something rather than be told about it. Instead of “She was nervous,” you show it: “Her hands wouldn't keep still, and she read the same line three times without taking it in.” Showing uses senses, actions and specific detail to make a scene vivid and let the reader feel the emotion for themselves.

It's one of the highest-value techniques in exam writing because it lifts both your ideas and your vocabulary at once — but it works best in small doses, on the moments that matter most.