create: ssh git@gitern.com gitern-create <path>
delete: ssh git@gitern.com gitern-delete <path>
list: ssh git@gitern.com gitern-list [<path>]
pubkey add: ssh git@gitern.com gitern-pubkey-add <account> (pubkey on stdin)
pubkey remove: ssh git@gitern.com gitern-pubkey-remove <SHA256 fingerprint> <account>
pubkey list: ssh git@gitern.com gitern-pubkey-list
Edit: Eventually the cli will provide a lot more (and self document what's available) so I do recommend using it, but you can happily get along with these "raw" commands for now.