1. Start with setting up a new backup and follow the wizard until you can select a place to store your backups
  2. Choose Amazon S3 based
  3. Fill out the highlighted fields as shown below with your credentials. Even if they look like a dropdown, you can type tekst.
  4. Fill out a unique bucketname and click on "Create bucket" or use one you created earlier.
  5. Complete the wizard

Setup 1

You can download Duplicati at: http://www.duplicati.com
Create a daDup account