do I input this somewhere on the admin panel?
No, you wait until they've propagated - which can take from several hours up to 72 hours. Unfortunately, there's no way to speed that up - it's how domain names work (not just WP).
Then you should be able to login to your site on GoDaddy and install that theme...
But just to be sure, you DO have WP installed on GoDaddy? Your site isn't on WordPress.COM?