A forwarder automatically redirects email sent to an address at your hosting account to an address elsewhere, such as your mailbox at your internet service provider.
A common use of forwarders is when your customers send all of their requests for information to the email address at your hosting account, you could use a forwarder so that all of the messages sent to that address are automatically forwarded to your personal email account at yourname@yourisp.com.
eg.
The forwarder "address@your-account.com" will redirect email to the destination "address@hotmail.com".