I am able to create a new quiz, and am then informed that 'no questons have been added ...'. I can't see how to add them! There doesn't seem to be an option that handles this.
The screen where you see 'no questons have been added ...' is split into two halves. The left one contains the quiz questions (empty), and the right one is a question bank (question pool, repository, whatever you call it). The question bank is divided into categories. You first need to select the category you want to use, or create one. Then add questions to this category. When you've created the questions, check the boxes next to the questions you want to use in your quiz, press the "add selected to quiz" button and you're home and dry.
Just put the text from Przemyslaw Stencel on that screen the problem is solved. I remember that I had to puzzle too the first time. (Do not hide it behind a help-button, just in line)
This side of the page is where you manage your database of questions. Questions are stored in categories to help you keep them organised, and can be used by any quiz in your course or even other courses if you choose to 'publish' them.
After you select or create a question category you will be able to create or edit questions. You can select any of these questions to add to your quiz over on the other side of this page.