When you set up your account for the first time, you are given access to your root public and secret access keys. These keys will be useful as you manage data on S3 and models in Amazon ML via the command line interface (AWS CLI). These two keys will only be available for you to view and copy at the time of creation. Once that page in your browser is closed, you can no longer access them and will need to create new ones. Creating new root keys is done by accessing My Account | Security Credentials. It's worth noting that no one can have access to your keys in AWS, not even the administrator of your account.
We won't go through all the possible actions you can take in IAM to configure, manage, and secure access to your account as a full presentation of IAM is beyond the scope of this book. Your access management needs and policies will depend on the size of your organization and security...