If you’re looking for a S3 client, check out Cyberduck. It’s a free FTP, SFTP, WebDAV, S3 & OpenStack Swift browser for both Mac and Windows. I started using it primarily to access an Amazon S3 account. Just download the client and select Amazon S3 to access your account.
You will need an Access Key ID and your Secret Access Key for your S3 account. You can get that from the AWS Dashboard under IAM (Identity Access Management). Once you’re authenticated, you can access your files from within Cyberduck. Drag and drop to download and upload. Very simple and intuitive.