Tutorials are lessons that take the reader by the hand through a series of steps to complete a project of some kind. They are what your project needs in order to show a beginner that they can achieve something with it. page 
They are wholly learning-oriented, and specifically, they are oriented towards learning how rather than learning that. You are the teacher, and you are responsible for what the student will do. Under your instruction, the student will execute a series of actions to achieve some end. The end and the actions are up to you, but deciding what they should be can be hard work. The end has to be meaningful, but also achievable for a complete beginner. The important thing is that having done the tutorial, the learner is in a position to make sense of the rest of the documentation, and the software itself.
Most software projects have really bad – or non-existent – tutorials. Tutorials are what will turn your learners into users. A bad or missing tutorial will prevent your project from acquiring new users.
Of the sections describing the four kinds of documentation, this is by far the longest – that’s because tutorials are the most misunderstood and most difficult to do well. The best way of teaching is to have a teacher present, interacting with the student. That’s rarely possible, and our written tutorials will be at best a far-from-perfect substitute. That’s all the more reason to pay special attention to them.
Tutorials need to be useful for the beginner, easy to follow, meaningful and extremely robust, and kept up-to-date. You might well find that writing and maintaining your tutorials can occupy as much time and energy as the other three parts put together.