If you get an email like this one, you have been invited to be part of an organization:
Once you click on the "Set up account" button, you'll be redirected to the user setup page. Before that, for security reasons, you'll be asked to confirm your email address.
Once you followed that step, you'll get to the setup form.
Here, you can set your Rambox password and modify your name. When you are satisfied with your data, just click on "Create" to set up your user. You'll see the following screen once your user is successfully created. You'll also get the possibility to download our installers from it.
To know how to get logged IN your organization in the Rambox desktop app please look at this ARTICLE.