To forward an additional URL through GoDaddy
1) Log on to your GoDaddy.com account
2) Click on the My Account button on the top left of your browser
3) Click Domains
4) Select the URL you wish to forward to your website by clicking the launch button under the action column
5) Click on Manage in the Forwarding Field
6) Enter your primary domain in the field and click ok when finished.
example if you are forwarding domainb.com to domaina.com you would enter domaina.com in this field