Fortunately, QuizNinja is easy to use, but here are some tutorials in case you're stuck...
How to Register
How to Login
How to Set Up a Course
How to add a Quiz and Questions
How to Add Games
How to Check Student Scores
How to Share Quizzes or Games with Colleagues
How to Get Shared Quizzes or Games
How to Use the QuestionBank
How to Use the Game Banks
Getting started: Adding Courses, Quizzes, and Questions!