You must define a secure key pair to be able to connect securely to your instance via SSH.
Navigate to the Key pair (login) section of the instance configuration page, then
select an existing key pair by name using the dropdown list, or select Create new
key pair to open a window where you can create a new secure key pair.
Tip: For detailed information about Amazon EC2 Key Pairs, refer to http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-key-pairs.html.
After selecting or creating a secure key pair, proceed to the Network settings section.