I followed DigitalOcean\'s tutorials on how to set up your server with SSH, creating a new user, firewalls etc. The first tutorial in the series is linked under:
htt
Digital ocean sets up your basic firewall with the '1-click' LAMP stack. All ports but ssh and http are blocked. I think the tutorial has you setting that up as well.
Run sudo ufw status
to see what ports are currently allowed
and then sudo ufw allow 10000/tcp
to allow access to the one webmin needs.