Keep the backup phrase you see at installation in a safe place. Lose phrase = lose Guldens. Someone else with access to the phrase = lose Guldens.
When you download the Gulden app, you explicitly and unconditionally agree that you are solely responsible for managing your Gulden and that use of the Gulden app is at your own risk. No rights can be derived from the use of the Gulden app towards Gulden.com B.V. In no event shall Gulden.com B.V. be liable for any damages whatsoever arising from the use of the app or the inability to use this app.