How do I make questions required or optional?

Forms cannot be submitted unless all required fields have been answered, with the exception of questions hidden with conditional logic. When your forms have multiple pages, submitters can't proceed to the next page until all visible, required fields on the current page are answered.

To change whether a question is required, click the question to open the configuration panel and toggle "Question is required" on/off.

The "Question is required" toggle can be found in the configuration panel - accessed by clicking a question.