These SSH keys allow you to SSH into a production device through the Balena VPN. This is done with the balena CLI by running balena ssh <device-uuid>. Any public SSH keys added to Balena Cloud can then be used to authenticate your login to the specified device. The <device-uuid> can be found using balena devices. Also balena ssh also allows you to specify a container to ssh into as well with balena ssh <device-uuid> <container-name>.
Let me know if you have any other questions about this information!