SSH keys are stored in your user account, and will let you access any instance which you have permission to access. If you've not generated one, we've a guide here.
You can upload a key from your user-profile, which you can find on our dashboard by clicking the little man icon, and then selecting profile.
Once there, click the 'Manage SSH Keys' bar, just below your user data;
From there, you can see, or remove, any of your SSH keys.
The "Key Name" is just a short descriptive name for you. The Public Key is where you paste the long public key string. If you're not sure you have one, you can find our guide on creating a new one here