To access your instances using SSH, generate at least one SSH key pair just as you did during the initial service registration. You can use any SSH utility to generate SSH keys and to log in to your instances. For example, if you're logging in from a Windows host, you can use PuTTY. If you're using a Linux host, you can use OpenSSH.
See Generate an SSH Key Pair on Oracle Solaris for an example.
Use the private key to log in to the instances using SSH.
Caution - Keep your SSH keys secure. Establish policies to ensure that the keys aren't lost or compromised when employees leave the organization or move to other departments. If you lose your private key, you can't access your instances. For business continuity, ensure that the SSH keys of at least two IT system administrators are added to your instances.