Quizzes are a new post type. To create a quiz, go to the forum page and click the Add Post button (➕) next to the search button. Select 'Quiz' instead of 'Post' and you can add questions/items to the quiz.

You can ask four types of questions:

Single: Select one answer choice.
Multiple: Select one or more answer choices.
Input: Enter text answer. You are allowed to specify multiple correct answers and whether the answer is case sensitive.
Match: Match the text value or image src to the text target.

Furthermore, there are two types of quizzes:

Trivia: Answer or pass, questions implement strict grading (it is either all right or all wrong), and scores are not saved.
Graded: You can navigate back and forth, questions implement strict grading and/or partial credit, scores (attempts) are saved. Quiz takers will only see their scores, but the post creator will see all scores.

A Note about Editing
Modifying quiz items can only be done through the classic markup system and not the forum's 'Create a Thread' mode. To edit your quiz, right-click and open in a new tab.

Here's a shitty demo quiz to give to you an idea of a graded quiz.