Hi, don't worry, I'm new to server management too.
Your base user is root in DigitalOcean, and if you made use of a RSA KEY You need to link to your Dropplet in some way, using the Droplet creation link,or copying your public key to the /.ssh/authorized_keys file. If you use the first way, you don't need to put the authorized_keys content.
The you need to modify your /etc/ssh/sshd_config file and change the line of PermitRootLogin yes to no.
Finally, save your changes and restart SSH service using:
sudo services ssh restart
Then try connecting with the command I recommended you before. You may need write your paragraph password as needed (not the user default password)
By default, your key should be named as id_rsa, if I'm not wrong.