# Overview

> A lesson is made of bricks, one per screen. Here's every kind and when your agent uses it.

A **brick** is one screen of a lesson. There are two families:

* **Concept bricks** teach: a short title, a few sentences, and often a visual.
* **Question bricks** practise: you answer, check, and get feedback.

Your agent picks each question brick by asking how a good teacher would test that point, not to fill a quota. Every page below has a live demo you can play.

| Brick                             | You…                      | Good for                                         |
| --------------------------------- | ------------------------- | ------------------------------------------------ |
| [Concept](https://learn.ninja/docs/bricks/concept)   | read                      | One idea, with a visual, formula, or code        |
| [Choice](https://learn.ninja/docs/bricks/choice)     | pick one or more answers  | Facts, rules, predictions                        |
| [Compare](https://learn.ninja/docs/bricks/compare)   | pick the better of two    | Judgement: which is clearer, safer, stronger     |
| [Hotspot](https://learn.ninja/docs/bricks/hotspot)   | tap the right spot        | Finding the problem in a UI, a document, or code |
| [Sort](https://learn.ninja/docs/bricks/sort)         | drag items into groups    | Telling categories apart                         |
| [Order](https://learn.ninja/docs/bricks/order)       | drag items into order     | Steps, sequences, ranking                        |
| [Match](https://learn.ninja/docs/bricks/match)       | link pairs                | Words and meanings, terms and definitions        |
| [Blank](https://learn.ninja/docs/bricks/blank)       | fill gaps with word chips | Sentences, formulas, code                        |
| [Scenario](https://learn.ninja/docs/bricks/scenario) | choose what to do         | Applying the idea to a realistic situation       |

## Every question brick has

* A **prompt** of up to 40 words.
* An **explanation**, shown after a correct answer (on request) or once the answer is revealed.
* **Feedback** on each wrong option that explains the mistake behind it.
* An optional **hint**, and an optional **visual**.

See [Lesson format](https://learn.ninja/docs/lessons/lesson-format) for every field.