1. you need to make a change to your DNS settings.

where every you registered your domain, you ned to change your Arecord to point at the correct ip number

2. you need to do a 301 redirect to primary domain.

DNS, resolves a name to a ip number,

that ip number should route to your website. Inthe headers of the resquest is the domain name, your web site should be configured to accept either all requests on a ip number and port or filtered by host headers (domains names), add all teh host headers needed, then in htaccess 30 to the pirmary domain name.

Good work Holmes

i have to correct you,

google sees this as one word some_keyword

but sees this as 2 words some-keyword

See link Donford posted

http://www.youtube.com/watch?v=Q3SFVfDIS5k