When I want to download certain things I've to be logged in. How do I create an account?
The account is created automatically. The initial credentials are delivered to your email together with the license key. You can change them after logging in.
You can log in here: https://www.softwareideas.net/Account/Login
Does that mean that as a non-commercial user you're not able to download any example files?
The additional resources such as style sets, diagram examples, and templates are available as extra content to any purchased copy of the software. Unfortunately, it is not available for all users. The free edition includes an example project - it is available from the File menu / Help / Example Project.