Email forwarding is an email address @ your domain name (e.g. bill@microsft.com) that automatically forwards all received emails to your existing email account (any other email address -e.g. my-other-email@gmail.com).

So if an email message is sent to bill@microsoft.com, a copy of that email would be sent automatically to any other email you set the email forwarding option to (e.g my-other-email@gmail.com).