The security group settings are important as they control who can access the instance, and where they can access it from. The Source tab allows you to set the machines that can connect to the instance, using IP addresses to determine who is allowed to connect:

For security, adjust the Source for SSH to my IP. This can be updated later to allow for connections from anywhere, that is the internet at large. Once that is complete, assign the existing key pair to the instance to ensure that it can be used for direct connections to the command line MapD Core.