S3 doesn't really have any notion of "files" and "folders".  Just objects.  While many tools (including the AWS Management Console) shows it as a folder-like structure, you fetch objects by their key which includes the full path (minus the bucket) to the object.

    s3://bucket-name/some/path/to/file.tar.gz

So to get the ```file.tar.gz``` you need to request the object by its key: ```some/path/to/file.tar.gz```