In the new Developer Manual, there is a whole section describing how to write a custom module - the Contacts module (Building a Module is the title). You may be familiar with this module from the Sitefinity blogs. The explanation is spread throughout 6 topics. Please let us know how exactly you expect the tutorial to go through these steps - do you prefer more code, do you prefer more theoretical explanation on how such a module could be implemented in Sitefinity, do you need more specific code examples.
Your opinion is very important for improving the documentation.
the Telerik team