I found on Safari Books online a great introductory video tutorial on Node, Express and MongoDB. Many screencasts say they're for beginners but are actually hard to follow or assume you know a lot before you can start. This screencast by Brad Traversy of Traversy Media is really good. I've been able to follow along and really learn step by step.
It begins with a simple CRUD app and then it progressively gets more complex. It ends up with user registration, OAUTH and even security. But if you are a real beginner you can learn from this video.
BTW: Safari Books Online has a 10 day free trial. Go and use it!