Online external new site urls not working.

I created a farm, then created my first site and I can access it online at:
http://mysite.com/SitePages/Home.aspx

But then I created another site called "testsite3"
I tried these external links online and none work?

http://mysite.com/testsite3
http://mysite.com/sites/testsite3

But when I am on the windows server box the internal link to the site works here:
http://myserver/sites/testsite3

Do I need to create Alternate Access Mapping to make additional sites work outside or externally? Or is the first site the only site can live on port 80?