If you have an ssh key set up in your DigitalOcean account, then that is the key set up on the root account. If not, you should have received a password email from DigitalOcean -- use that.
You might be more interested in installing our church app OneBody. You can do that by clicking the "Install on DigitalOcean" button in the readme here: https://github.com/churchio/onebody