how does a packet get to a new site

The title should be how does a packet get to a computer it has never communicated with before??? I know that it uses broadcasting but , say for example, I want to communicate with a computer in australia by sending an email message, but have never sent one before???I dont know Ip or mac address of either one. I get the email address from someone else, How does the packet find the right computer??? I need to know this for the cisco exam.
Thanks