To set up Checklist questions, select a checklist and click on the Questions tab. Then click on + New Question. 

A pop up box will be displayed which gives you an option of whether you would like to select a question from the Question Library (this is a full listing of all the questions you have used in the past from all your checklists) or whether you would like to create a new question.

If you want to choose an existing question/s, you can select all the questions you would like to include and click on Add.

To create a new question, click on Create a new Question and you will be able to create a new question using a variety of types of fields. 

If you want to create multiple questions, click on Create and New.