Storage Plugin: Amazon S3

You can retrieve AWS Access Key and AWS Secret Key in your account on Amazon in section:

Services > IAM (Identity and Access Management) > Users > Add User

AWS access type: Programmatic access

You need to grant "AmazonS3FullAccess" to this Access Key, or if you are familiar with AWS, assign full permissions only for a particular S3 bucket, + list-buckets permission for all buckets.