While it is possible to manage your servers using password-based logins, it is often a better idea to set up and use SSH key pairs. SSH keys are more secure than passwords, and can help you log in without having to remember long passwords.
To use SSH keys with your Droplets, you need to:
Add your SSH key to your Droplets. On DigitalOcean, you can upload your SSH public key to your account, which lets you add it to your Droplets at creation time. This lets you log into your servers without a password while still remaining secure. You can also upload your keys manually after creation.