One quick way of getting started with writing a module is to install a stub module, and then customize it to do what you want. Doing so saves you from having to create numerous directories, figure out which files go where, or remembering which methods you need to implement to get started.
This recipe shows you how you can get started quickly using the Skeleton module.
For this recipe, you will need to have login access to the site's Administration area with permission to "Modify Modules" and "Manage All Content".
You will also need write access to the filesystem of the server where your CMS is installed. This recipe assumes you are using SSH to access the server, but other approaches ...