How can I add random questions to my quiz/exam?
You should select the button "Add a random question" located at the bottom of your quiz test.
If you want your entire quiz/exam to have random questions, then do not add any questions to the test. Instead, go to the bottom of your quiz bank, and list the number of random questions you want to move to the quiz/exam. Remember that you should have a greater number of questions in your bank than you do within your quiz/exam to make an effective test.