Log in to your godaddy account manager and register two host records for firstdomain.com
where xxx.xxx.xxx.xxx and yyy.yyy.yyy.yyy are ip address of your hosting server. It is not necessary to have 2 different ips you can use one for both records.
Read following manual for details: http://support.godaddy.com/help/article/668/registering-your-own-nameservershosts
Once this has been done, login to vesta control panel.
Add firstdomain.com with "DNS support" mark checked.
Go to DNS tab and click on "add record".
Add new record
IP or Value: xxx.xxx.xxx.xxx
and the second one
IP or Value: yyy.yyy.yyy.yyy
Now click on "Back" button and then click on "list records" under firstdomain.com
Find 2 NS records "ns1.localhost.ltd." and "ns2.localhost.ltd." Edit and replace them with "ns1.firstdomain.com." and "firstdomain.com." accordingly. Please make sure you put trailing dot in the end.
At this point dns setup for firstdomain.com is completed.
Go to USER tab and click on edit link to edit your user account settings. Set ns1.firstdomain.com and ns2.firstdomain.com as a "Default Name Servers" and click "Save". Congratulations, you are ready to go!
Let's see how to add second or third or any other domain.
1. Log in to your godaddy account manager.
2. Set ns1.firstdomain.com and ns2.firstdomain.com as name serverhttp://support.godaddy.com/help/article/664/setting-nameservers-for-your-domain-names
3. Open vesta control panel
4. Add domain with DNS support check mark selected.