Create a new key pair, if needed

Open a terminal and run the following command:

ssh-keygen

You will be prompted to save and name the key.Generating public/private rsa key pair. Enter file in which to save the key (/Users/USER/.ssh/id_rsa):

Next you will be asked to create and confirm a passphrase for the key (highly recommended):Enter passphrase (empty for no passphrase): 
Enter same passphrase again:

This will generate two files, by default called id_rsa and id_rsa.pub. Next, add this public key.

Add the public key

Copy and paste the contents of the .pub file, typically id_rsa.pub, into the SSH key contentfield on the left.

cat ~/.ssh/id_rsa.pub

For more detailed guidance, see How to Add SSH Keys to Droplets