In order for your domain name to point to your new web hosting account, you need to change the DNS information with your domain registrar (i.e. the place where you ordered your domain).
Most registrars will allow you to log in and manage your domain name(s) online. Once you have done this, find the section regarding "Nameservers" or "DNS". You should then be able to change the two nameservers for your domain to those specified in your welcome email (under the heading "DNS INFORMATION"). Your registrar may or may not require that you provide the corresponding Master and Secondary IP addresses also.
To find your name servers open up the email we sent you with the subject New Account Information