Select "Show one question at a time" in the Custom Test Builder (or when editing a custom test) to show applicants a single question at a time. They'll have to answer before moving onto the next question.
You might want to turn this feature on:
To prevent applicants from cheating by taking a screenshot of the entire test, reporting an issue, and then asking to retake the test after they've researched the answers. (If you are using the feature for this purpose, you should also turn on the option to randomize the question order.)
To allow applicants to focus on a single question at a time, which is especially useful for more complicated questions.
For more context, see our complete walk-through of the Custom Test Builder.