You will need to create whatever DNS Records you need to point whatever services\hostnames you want to the new VPS on the nameservers the domain in question is using - you cannot do this on the VPS (nor in Plesk if you have that installed)
If you want to point your website to the VPS then you need the following records:
domain.com - A - SERVERIP
*.domain.com - A - SERVERIP
If you want to point email to the VPS then you need the following records:
domain.com - MX - mail.domain.com
mail.domain.com - A - SERVERIP
Where SERVERIP is the IP address of your VPS (you can see it in billing.myhost.ie or get it from your welcome email)
