Permission denied (publickey) issue

I am new to Digital Ocean and I created a droplet using an SSH key with Puttygen. Now it seems I can’t login from the console as it requires a password to login and none of them works, I’ve tried my SSH key passphrase and the root password that has been e-mailed to me as I used the Reset Password function, and always get the Login Incorrect message.

So I used Putty instead and managed to login but I keep running into Permission Denied (publickey) issues, both as root and as the user I created. If I try to log in (ssh user@serverip), I get permission denied. I tried uploading a file on my server both as root and user and permission is denied. I tried to view the authorized keys to grant the necessary permissions as explained on this page (https://www.digitalocean.com/docs/droplets/resources/troubleshooting-ssh/authentication/#fixing-key-permissions-and-ownership) using the /root/.ssh/authorized_key command but I get permission denied here too.

I am not familiar enough with Linux and the system to understand where these authentication issues come from and what I would need to do to fix them and being able to access my server properly. Any help will be warmly appreciated.