Hi Daniel!
There is a user manual for the newsletter module here, where you get quite a bit of information:
http://www.webnodes.com/newsletter-user-manual
It doesn't detail the setup. The setup process contains these steps:
1. There are two types of newsletters: Basic and regular. The basic newsletter has a simple built-in template, and you basically write the whole content in an html editor, images and all. Good for simple newsletters, but not more advanced needs. When you add a basic newsletter, the system creates the template for you.
For regular newsletters, the setup is a bit more involved. First you must create a newsletter template in the template module. A newsletter template is just a regular template where you output email friendly html.
2. Then you can open the "Edit settings" menu item on the Settings menu in the newsletter module. Mark the content class(es) that can be used for the template you created in the first step, and thetemplate in the right column.
3. Create a subscriber list, and add the users and email you want. I often recommend creating a test list as well to use during development, where you can add a few of your own email addresses.
4. Create a newsletter. Fill all the relevant properties on the Newsletter, and select the subscriver list.
5. Send a test by clicking the "Make new delivery" button on top of the newsletter form, and fill in the details in the dialogue window that opens. Just make sure you don't send a test to the full subscriber list.