Hi, I am novice linux level but I think I can answer this :)

• first and most important you need to put your public key in .ssh folder on your client machine with 755 permission on in.
• if you disable password login on server your ssh credentials will be ssh username@ipofyourdroplet and password for your key if you add it on creation of your key pair
• if you have user/pass login active on you droplet your credential will be same as above but you need to enter your password for username and rest is same.

I hope this will help you